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| author | chai <chaifix@163.com> | 2021-10-30 11:32:16 +0800 |
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| committer | chai <chaifix@163.com> | 2021-10-30 11:32:16 +0800 |
| commit | 42ec7286b2d36a9ba22925f816a17cb1cc2aa5ce (patch) | |
| tree | 24bc7009457a8d7500f264e89946dc20d069294f /Data/Libraries/Penlight/docs/manual/06-data.md.html | |
| parent | 164885fd98d48703bd771f802d79557b7db97431 (diff) | |
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diff --git a/Data/Libraries/Penlight/docs/manual/06-data.md.html b/Data/Libraries/Penlight/docs/manual/06-data.md.html new file mode 100644 index 0000000..585e23e --- /dev/null +++ b/Data/Libraries/Penlight/docs/manual/06-data.md.html @@ -0,0 +1,1633 @@ +<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" + "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"> +<html> +<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"/> +<head> + <title>Penlight Documentation</title> + <link rel="stylesheet" href="../ldoc_fixed.css" type="text/css" /> +</head> +<body> + +<div id="container"> + +<div id="product"> + <div id="product_logo"></div> + <div id="product_name"><big><b></b></big></div> + <div id="product_description"></div> +</div> <!-- id="product" --> + + +<div id="main"> + + +<!-- Menu --> + +<div id="navigation"> +<br/> +<h1>Penlight</h1> + +<ul> + <li><a href="https://github.com/lunarmodules/Penlight">GitHub Project</a></li> + <li><a href="../index.html">Documentation</a></li> +</ul> + +<h2>Contents</h2> +<ul> +<li><a href="#Reading_Data_Files">Reading Data Files </a></li> +<li><a href="#Reading_Unstructured_Text_Data">Reading Unstructured Text Data </a></li> +<li><a href="#Reading_Columnar_Data">Reading Columnar Data </a></li> +<li><a href="#Reading_Configuration_Files">Reading Configuration Files </a></li> +<li><a href="#Lexical_Scanning">Lexical Scanning </a></li> +<li><a href="#XML">XML </a></li> +</ul> + + +<h2>Manual</h2> +<ul class="nowrap"> + <li><a href="../manual/01-introduction.md.html">Introduction</a></li> + <li><a href="../manual/02-arrays.md.html">Tables and Arrays</a></li> + <li><a href="../manual/03-strings.md.html">Strings. Higher-level operations on strings.</a></li> + <li><a href="../manual/04-paths.md.html">Paths and Directories</a></li> + <li><a href="../manual/05-dates.md.html">Date and Time</a></li> + <li><strong>Data</strong></li> + <li><a href="../manual/07-functional.md.html">Functional Programming</a></li> + <li><a href="../manual/08-additional.md.html">Additional Libraries</a></li> + <li><a href="../manual/09-discussion.md.html">Technical Choices</a></li> +</ul> +<h2>Libraries</h2> +<ul class="nowrap"> + <li><a href="../libraries/pl.html">pl</a></li> + <li><a href="../libraries/pl.app.html">pl.app</a></li> + <li><a href="../libraries/pl.array2d.html">pl.array2d</a></li> + <li><a href="../libraries/pl.class.html">pl.class</a></li> + <li><a href="../libraries/pl.compat.html">pl.compat</a></li> + <li><a href="../libraries/pl.comprehension.html">pl.comprehension</a></li> + <li><a href="../libraries/pl.config.html">pl.config</a></li> + <li><a href="../libraries/pl.data.html">pl.data</a></li> + <li><a href="../libraries/pl.dir.html">pl.dir</a></li> + <li><a href="../libraries/pl.file.html">pl.file</a></li> + <li><a href="../libraries/pl.func.html">pl.func</a></li> + <li><a href="../libraries/pl.import_into.html">pl.import_into</a></li> + <li><a href="../libraries/pl.input.html">pl.input</a></li> + <li><a href="../libraries/pl.lapp.html">pl.lapp</a></li> + <li><a href="../libraries/pl.lexer.html">pl.lexer</a></li> + <li><a href="../libraries/pl.luabalanced.html">pl.luabalanced</a></li> + <li><a href="../libraries/pl.operator.html">pl.operator</a></li> + <li><a href="../libraries/pl.path.html">pl.path</a></li> + <li><a href="../libraries/pl.permute.html">pl.permute</a></li> + <li><a href="../libraries/pl.pretty.html">pl.pretty</a></li> + <li><a href="../libraries/pl.seq.html">pl.seq</a></li> + <li><a href="../libraries/pl.sip.html">pl.sip</a></li> + <li><a href="../libraries/pl.strict.html">pl.strict</a></li> + <li><a href="../libraries/pl.stringio.html">pl.stringio</a></li> + <li><a href="../libraries/pl.stringx.html">pl.stringx</a></li> + <li><a href="../libraries/pl.tablex.html">pl.tablex</a></li> + <li><a href="../libraries/pl.template.html">pl.template</a></li> + <li><a href="../libraries/pl.test.html">pl.test</a></li> + <li><a href="../libraries/pl.text.html">pl.text</a></li> + <li><a href="../libraries/pl.types.html">pl.types</a></li> + <li><a href="../libraries/pl.url.html">pl.url</a></li> + <li><a href="../libraries/pl.utils.html">pl.utils</a></li> + <li><a href="../libraries/pl.xml.html">pl.xml</a></li> +</ul> +<h2>Classes</h2> +<ul class="nowrap"> + <li><a href="../classes/pl.Date.html">pl.Date</a></li> + <li><a href="../classes/pl.List.html">pl.List</a></li> + <li><a href="../classes/pl.Map.html">pl.Map</a></li> + <li><a href="../classes/pl.MultiMap.html">pl.MultiMap</a></li> + <li><a href="../classes/pl.OrderedMap.html">pl.OrderedMap</a></li> + <li><a href="../classes/pl.Set.html">pl.Set</a></li> +</ul> +<h2>Examples</h2> +<ul class="nowrap"> + <li><a href="../examples/seesubst.lua.html">seesubst.lua</a></li> + <li><a href="../examples/sipscan.lua.html">sipscan.lua</a></li> + <li><a href="../examples/symbols.lua.html">symbols.lua</a></li> + <li><a href="../examples/test-cmp.lua.html">test-cmp.lua</a></li> + <li><a href="../examples/test-data.lua.html">test-data.lua</a></li> + <li><a href="../examples/test-listcallbacks.lua.html">test-listcallbacks.lua</a></li> + <li><a href="../examples/test-pretty.lua.html">test-pretty.lua</a></li> + <li><a href="../examples/test-symbols.lua.html">test-symbols.lua</a></li> + <li><a href="../examples/testclone.lua.html">testclone.lua</a></li> + <li><a href="../examples/testconfig.lua.html">testconfig.lua</a></li> + <li><a href="../examples/testglobal.lua.html">testglobal.lua</a></li> + <li><a href="../examples/testinputfields.lua.html">testinputfields.lua</a></li> + <li><a href="../examples/testinputfields2.lua.html">testinputfields2.lua</a></li> + <li><a href="../examples/testxml.lua.html">testxml.lua</a></li> + <li><a href="../examples/which.lua.html">which.lua</a></li> +</ul> + +</div> + +<div id="content"> + + +<h2>Data</h2> + +<p><a name="Reading_Data_Files"></a></p> +<h3>Reading Data Files</h3> + +<p>The first thing to consider is this: do you actually need to write a custom file +reader? And if the answer is yes, the next question is: can you write the reader +in as clear a way as possible? Correctness, Robustness, and Speed; pick the first +two and the third can be sorted out later, <em>if necessary</em>.</p> + +<p>A common sort of data file is the configuration file format commonly used on Unix +systems. This format is often called a <em>property</em> file in the Java world.</p> + + +<pre> +# Read timeout <span class="keyword">in</span> seconds +read.timeout=<span class="number">10</span> + +# Write timeout <span class="keyword">in</span> seconds +write.timeout=<span class="number">10</span> +</pre> + +<p>Here is a simple Lua implementation:</p> + + +<pre> +<span class="comment">-- property file parsing with Lua string patterns +</span>props = [] +<span class="keyword">for</span> line <span class="keyword">in</span> <span class="global">io</span>.lines() <span class="keyword">do</span> + <span class="keyword">if</span> line:find(<span class="string">'#'</span>,<span class="number">1</span>,<span class="keyword">true</span>) ~= <span class="number">1</span> <span class="keyword">and</span> <span class="keyword">not</span> line:find(<span class="string">'^%s*$'</span>) <span class="keyword">then</span> + <span class="keyword">local</span> var,value = line:match(<span class="string">'([^=]+)=(.*)'</span>) + props[var] = value + <span class="keyword">end</span> +<span class="keyword">end</span> +</pre> + +<p>Very compact, but it suffers from a similar disease in equivalent Perl programs; +it uses odd string patterns which are 'lexically noisy'. Noisy code like this +slows the casual reader down. (For an even more direct way of doing this, see the +next section, 'Reading Configuration Files')</p> + +<p>Another implementation, using the Penlight libraries:</p> + + +<pre> +<span class="comment">-- property file parsing with extended string functions +</span><span class="global">require</span> <span class="string">'pl'</span> +stringx.import() +props = [] +<span class="keyword">for</span> line <span class="keyword">in</span> <span class="global">io</span>.lines() <span class="keyword">do</span> + <span class="keyword">if</span> <span class="keyword">not</span> line:startswith(<span class="string">'#'</span>) <span class="keyword">and</span> <span class="keyword">not</span> line:isspace() <span class="keyword">then</span> + <span class="keyword">local</span> var,value = line:splitv(<span class="string">'='</span>) + props[var] = value + <span class="keyword">end</span> +<span class="keyword">end</span> +</pre> + +<p>This is more self-documenting; it is generally better to make the code express +the <em>intention</em>, rather than having to scatter comments everywhere - comments are +necessary, of course, but mostly to give the higher view of your intention that +cannot be expressed in code. It is slightly slower, true, but in practice the +speed of this script is determined by I/O, so further optimization is unnecessary.</p> + +<p><a name="Reading_Unstructured_Text_Data"></a></p> +<h3>Reading Unstructured Text Data</h3> + +<p>Text data is sometimes unstructured, for example a file containing words. The +<a href="../libraries/pl.input.html#">pl.input</a> module has a number of functions which makes processing such files +easier. For example, a script to count the number of words in standard input +using <code>import.words</code>:</p> + + +<pre> +<span class="comment">-- countwords.lua +</span><span class="global">require</span> <span class="string">'pl'</span> +<span class="keyword">local</span> k = <span class="number">1</span> +<span class="keyword">for</span> w <span class="keyword">in</span> input.words(<span class="global">io</span>.stdin) <span class="keyword">do</span> + k = k + <span class="number">1</span> +<span class="keyword">end</span> +<span class="global">print</span>(<span class="string">'count'</span>,k) +</pre> + +<p>Or this script to calculate the average of a set of numbers using <a href="../libraries/pl.input.html#numbers">input.numbers</a>:</p> + + +<pre> +<span class="comment">-- average.lua +</span><span class="global">require</span> <span class="string">'pl'</span> +<span class="keyword">local</span> k = <span class="number">1</span> +<span class="keyword">local</span> sum = <span class="number">0</span> +<span class="keyword">for</span> n <span class="keyword">in</span> input.numbers(<span class="global">io</span>.stdin) <span class="keyword">do</span> + sum = sum + n + k = k + <span class="number">1</span> +<span class="keyword">end</span> +<span class="global">print</span>(<span class="string">'average'</span>,sum/k) +</pre> + +<p>These scripts can be improved further by <em>eliminating loops</em> In the last case, +there is a perfectly good function <a href="../libraries/pl.seq.html#sum">seq.sum</a> which can already take a sequence of +numbers and calculate these numbers for us:</p> + + +<pre> +<span class="comment">-- average2.lua +</span><span class="global">require</span> <span class="string">'pl'</span> +<span class="keyword">local</span> total,n = seq.sum(input.numbers()) +<span class="global">print</span>(<span class="string">'average'</span>,total/n) +</pre> + +<p>A further simplification here is that if <code>numbers</code> or <code>words</code> are not passed an +argument, they will grab their input from standard input. The first script can +be rewritten:</p> + + +<pre> +<span class="comment">-- countwords2.lua +</span><span class="global">require</span> <span class="string">'pl'</span> +<span class="global">print</span>(<span class="string">'count'</span>,seq.count(input.words())) +</pre> + +<p>A useful feature of a sequence generator like <code>numbers</code> is that it can read from +a string source. Here is a script to calculate the sums of the numbers on each +line in a file:</p> + + +<pre> +<span class="comment">-- sums.lua +</span><span class="keyword">for</span> line <span class="keyword">in</span> <span class="global">io</span>.lines() <span class="keyword">do</span> + <span class="global">print</span>(seq.sum(input.numbers(line)) +<span class="keyword">end</span> +</pre> + +<p><a name="Reading_Columnar_Data"></a></p> +<h3>Reading Columnar Data</h3> + +<p>It is very common to find data in columnar form, either space or comma-separated, +perhaps with an initial set of column headers. Here is a typical example:</p> + + +<pre> +EventID Magnitude LocationX LocationY LocationZ +<span class="number">981124001</span> <span class="number">2.0</span> <span class="number">18988.4</span> <span class="number">10047.1</span> <span class="number">4149.7</span> +<span class="number">981125001</span> <span class="number">0.8</span> <span class="number">19104.0</span> <span class="number">9970.4</span> <span class="number">5088.7</span> +<span class="number">981127003</span> <span class="number">0.5</span> <span class="number">19012.5</span> <span class="number">9946.9</span> <span class="number">3831.2</span> +... +</pre> + +<p><a href="../libraries/pl.input.html#fields">input.fields</a> is designed to extract several columns, given some delimiter +(default to whitespace). Here is a script to calculate the average X location of +all the events:</p> + + +<pre> +<span class="comment">-- avg-x.lua +</span><span class="global">require</span> <span class="string">'pl'</span> +<span class="global">io</span>.read() <span class="comment">-- skip the header line +</span><span class="keyword">local</span> sum,count = seq.sum(input.fields {<span class="number">3</span>}) +<span class="global">print</span>(sum/count) +</pre> + +<p><a href="../libraries/pl.input.html#fields">input.fields</a> is passed either a field count, or a list of column indices, +starting at one as usual. So in this case we're only interested in column 3. If +you pass it a field count, then you get every field up to that count:</p> + + +<pre> +<span class="keyword">for</span> id,mag,locX,locY,locZ <span class="keyword">in</span> input.fields (<span class="number">5</span>) <span class="keyword">do</span> +.... +<span class="keyword">end</span> +</pre> + +<p><a href="../libraries/pl.input.html#fields">input.fields</a> by default tries to convert each field to a number. It will skip +lines which clearly don't match the pattern, but will abort the script if there +are any fields which cannot be converted to numbers.</p> + +<p>The second parameter is a delimiter, by default spaces. ' ' is understood to mean +'any number of spaces', i.e. '%s+'. Any Lua string pattern can be used.</p> + +<p>The third parameter is a <em>data source</em>, by default standard input (defined by +<a href="../libraries/pl.input.html#create_getter">input.create_getter</a>.) It assumes that the data source has a <code>read</code> method which +brings in the next line, i.e. it is a 'file-like' object. As a special case, a +string will be split into its lines:</p> + + +<pre> +> <span class="keyword">for</span> x,y <span class="keyword">in</span> input.fields(<span class="number">2</span>,<span class="string">' '</span>,<span class="string">'10 20\n30 40\n'</span>) <span class="keyword">do</span> <span class="global">print</span>(x,y) <span class="keyword">end</span> +<span class="number">10</span> <span class="number">20</span> +<span class="number">30</span> <span class="number">40</span> +</pre> + +<p>Note the default behaviour for bad fields, which is to show the offending line +number:</p> + + +<pre> +> <span class="keyword">for</span> x,y <span class="keyword">in</span> input.fields(<span class="number">2</span>,<span class="string">' '</span>,<span class="string">'10 20\n30 40x\n'</span>) <span class="keyword">do</span> <span class="global">print</span>(x,y) <span class="keyword">end</span> +<span class="number">10</span> <span class="number">20</span> +line <span class="number">2</span>: cannot convert <span class="string">'40x'</span> to number +</pre> + +<p>This behaviour of <a href="../libraries/pl.input.html#fields">input.fields</a> is appropriate for a script which you want to +fail immediately with an appropriate <em>user</em> error message if conversion fails. +The fourth optional parameter is an options table: <code>{no_fail=true}</code> means that +conversion is attempted but if it fails it just returns the string, rather as AWK +would operate. You are then responsible for checking the type of the returned +field. <code>{no_convert=true}</code> switches off conversion altogether and all fields are +returned as strings.</p> + + +<p>Sometimes it is useful to bring a whole dataset into memory, for operations such +as extracting columns. Penlight provides a flexible reader specifically for +reading this kind of data, using the <a href="../libraries/pl.data.html#">data</a> module. Given a file looking like this:</p> + + +<pre> +x,y +<span class="number">10</span>,<span class="number">20</span> +<span class="number">2</span>,<span class="number">5</span> +<span class="number">40</span>,<span class="number">50</span> +</pre> + +<p>Then <a href="../libraries/pl.data.html#read">data.read</a> will create a table like this, with each row represented by a +sublist:</p> + + +<pre> +> t = data.read <span class="string">'test.txt'</span> +> pretty.dump(t) +{{<span class="number">10</span>,<span class="number">20</span>},{<span class="number">2</span>,<span class="number">5</span>},{<span class="number">40</span>,<span class="number">50</span>},fieldnames={<span class="string">'x'</span>,<span class="string">'y'</span>},delim=<span class="string">','</span>} +</pre> + +<p>You can now analyze this returned table using the supplied methods. For instance, +the method <a href="../libraries/pl.data.html#Data.column_by_name">column_by_name</a> returns a table of all the values of that column.</p> + + +<pre> +<span class="comment">-- testdata.lua +</span><span class="global">require</span> <span class="string">'pl'</span> +d = data.read(<span class="string">'fev.txt'</span>) +<span class="keyword">for</span> _,name <span class="keyword">in</span> <span class="global">ipairs</span>(d.fieldnames) <span class="keyword">do</span> + <span class="keyword">local</span> col = d:column_by_name(name) + <span class="keyword">if</span> <span class="global">type</span>(col[<span class="number">1</span>]) == <span class="string">'number'</span> <span class="keyword">then</span> + <span class="keyword">local</span> total,n = seq.sum(col) + utils.printf(<span class="string">"Average for %s is %f\n"</span>,name,total/n) + <span class="keyword">end</span> +<span class="keyword">end</span> +</pre> + +<p><a href="../libraries/pl.data.html#read">data.read</a> tries to be clever when given data; by default it expects a first +line of column names, unless any of them are numbers. It tries to deduce the +column delimiter by looking at the first line. Sometimes it guesses wrong; these +things can be specified explicitly. The second optional parameter is an options +table: can override <code>delim</code> (a string pattern), <code>fieldnames</code> (a list or +comma-separated string), specify <code>no_convert</code> (default is to convert), numfields +(indices of columns known to be numbers, as a list) and <code>thousands_dot</code> (when the +thousands separator in Excel CSV is '.')</p> + +<p>A very powerful feature is a way to execute SQL-like queries on such data:</p> + + +<pre> +<span class="comment">-- queries on tabular data +</span><span class="global">require</span> <span class="string">'pl'</span> +<span class="keyword">local</span> d = data.read(<span class="string">'xyz.txt'</span>) +<span class="keyword">local</span> q = d:<span class="global">select</span>(<span class="string">'x,y,z where x > 3 and z < 2 sort by y'</span>) +<span class="keyword">for</span> x,y,z <span class="keyword">in</span> q <span class="keyword">do</span> + <span class="global">print</span>(x,y,z) +<span class="keyword">end</span> +</pre> + +<p>Please note that the format of queries is restricted to the following syntax:</p> + + +<pre> +FIELDLIST [ <span class="string">'where'</span> CONDITION ] [ <span class="string">'sort by'</span> FIELD [asc|desc]] +</pre> + +<p>Any valid Lua code can appear in <code>CONDITION</code>; remember it is <em>not</em> SQL and you +have to use <code>==</code> (this warning comes from experience.)</p> + +<p>For this to work, <em>field names must be Lua identifiers</em>. So <a href="../libraries/pl.data.html#read">read</a> will massage +fieldnames so that all non-alphanumeric chars are replaced with underscores. +However, the <code>original_fieldnames</code> field always contains the original un-massaged +fieldnames.</p> + +<p><a href="../libraries/pl.data.html#read">read</a> can handle standard CSV files fine, although doesn't try to be a +full-blown CSV parser. With the <code>csv=true</code> option, it's possible to have +double-quoted fields, which may contain commas; then trailing commas become +significant as well.</p> + +<p>Spreadsheet programs are not always the best tool to +process such data, strange as this might seem to some people. This is a toy CSV +file; to appreciate the problem, imagine thousands of rows and dozens of columns +like this:</p> + + +<pre> +Department Name,Employee ID,Project,Hours Booked +sales,<span class="number">1231</span>,overhead,<span class="number">4</span> +sales,<span class="number">1255</span>,overhead,<span class="number">3</span> +engineering,<span class="number">1501</span>,development,<span class="number">5</span> +engineering,<span class="number">1501</span>,maintenance,<span class="number">3</span> +engineering,<span class="number">1433</span>,maintenance,<span class="number">10</span> +</pre> + +<p>The task is to reduce the dataset to a relevant set of rows and columns, perhaps +do some processing on row data, and write the result out to a new CSV file. The +<a href="../libraries/pl.data.html#Data.write_row">write_row</a> method uses the delimiter to write the row to a file; +<code>Data.select_row</code> is like <code>Data.select</code>, except it iterates over <em>rows</em>, not +fields; this is necessary if we are dealing with a lot of columns!</p> + + +<pre> +names = {[<span class="number">1501</span>]=<span class="string">'don'</span>,[<span class="number">1433</span>]=<span class="string">'dilbert'</span>} +keepcols = {<span class="string">'Employee_ID'</span>,<span class="string">'Hours_Booked'</span>} +t:write_row (outf,{<span class="string">'Employee'</span>,<span class="string">'Hours_Booked'</span>}) +q = t:select_row { + fields=keepcols, + where=<span class="keyword">function</span>(row) <span class="keyword">return</span> row[<span class="number">1</span>]==<span class="string">'engineering'</span> <span class="keyword">end</span> +} +<span class="keyword">for</span> row <span class="keyword">in</span> q <span class="keyword">do</span> + row[<span class="number">1</span>] = names[row[<span class="number">1</span>]] + t:write_row(outf,row) +<span class="keyword">end</span> +</pre> + +<p><code>Data.select_row</code> and <code>Data.select</code> can be passed a table specifying the query; a +list of field names, a function defining the condition and an optional parameter +<code>sort_by</code>. It isn't really necessary here, but if we had a more complicated row +condition (such as belonging to a specified set) then it is not generally +possible to express such a condition as a query string, without resorting to +hackery such as global variables.</p> + +<p>With 1.0.3, you can specify explicit conversion functions for selected columns. +For instance, this is a log file with a Unix date stamp:</p> + + +<pre> +Time Message +<span class="number">1266840760</span> +# EE7C0600006F0D00C00F06010302054000000308010A00002B00407B00 +<span class="number">1266840760</span> closure data <span class="number">0.000000</span> <span class="number">1972</span> <span class="number">1972</span> <span class="number">0</span> +<span class="number">1266840760</span> ++ <span class="number">1266840760</span> EE <span class="number">1</span> +<span class="number">1266840760</span> +# EE7C0600006F0D00C00F06010302054000000408020A00002B00407B00 +<span class="number">1266840764</span> closure data <span class="number">0.000000</span> <span class="number">1972</span> <span class="number">1972</span> <span class="number">0</span> +</pre> + +<p>We would like the first column as an actual date object, so the <code>convert</code> +field sets an explicit conversion for column 1. (Note that we have to explicitly +convert the string to a number first.)</p> + + +<pre> +Date = <span class="global">require</span> <span class="string">'pl.Date'</span> + +<span class="keyword">function</span> date_convert (ds) + <span class="keyword">return</span> Date(<span class="global">tonumber</span>(ds)) +<span class="keyword">end</span> + +d = data.read(f,{convert={[<span class="number">1</span>]=date_convert},last_field_collect=<span class="keyword">true</span>}) +</pre> + +<p>This gives us a two-column dataset, where the first column contains <a href="../classes/pl.Date.html#">Date</a> objects +and the second column contains the rest of the line. Queries can then easily +pick out events on a day of the week:</p> + + +<pre> +q = d:<span class="global">select</span> <span class="string">"Time,Message where Time:weekday_name()=='Sun'"</span> +</pre> + +<p>Data does not have to come from files, nor does it necessarily come from the lab +or the accounts department. On Linux, <code>ps aux</code> gives you a full listing of all +processes running on your machine. It is straightforward to feed the output of +this command into <a href="../libraries/pl.data.html#read">data.read</a> and perform useful queries on it. Notice that +non-identifier characters like '%' get converted into underscores:</p> + + +<pre> +<span class="global">require</span> <span class="string">'pl'</span> +f = <span class="global">io</span>.popen <span class="string">'ps aux'</span> +s = data.read (f,{last_field_collect=<span class="keyword">true</span>}) +f:close() +<span class="global">print</span>(s.fieldnames) +<span class="global">print</span>(s:column_by_name <span class="string">'USER'</span>) +qs = <span class="string">'COMMAND,_MEM where _MEM > 5 and USER=="steve"'</span> +<span class="keyword">for</span> name,mem <span class="keyword">in</span> s:<span class="global">select</span>(qs) <span class="keyword">do</span> + <span class="global">print</span>(mem,name) +<span class="keyword">end</span> +</pre> + +<p>I've always been an admirer of the AWK programming language; with <a href="../libraries/pl.data.html#filter">filter</a> you +can get Lua programs which are just as compact:</p> + + +<pre> +<span class="comment">-- printxy.lua +</span><span class="global">require</span> <span class="string">'pl'</span> +data.filter <span class="string">'x,y where x > 3'</span> +</pre> + +<p>It is common enough to have data files without headers of field names. +<a href="../libraries/pl.data.html#read">data.read</a> makes a special exception for such files if all fields are numeric. +Since there are no column names to use in query expressions, you can use AWK-like +column indexes, e.g. '$1,$2 where $1 > 3'. I have a little executable script on +my system called <code>lf</code> which looks like this:</p> + + +<pre> +#!/usr/bin/env lua +<span class="global">require</span> <span class="string">'pl.data'</span>.filter(arg[<span class="number">1</span>]) +</pre> + +<p>And it can be used generally as a filter command to extract columns from data. +(The column specifications may be expressions or even constants.)</p> + + +<pre> +$ lf <span class="string">'$1,$5/10'</span> < test.dat +</pre> + +<p>(As with AWK, please note the single-quotes used in this command; this prevents +the shell trying to expand the column indexes. If you are on Windows, then you +must quote the expression in double-quotes so +it is passed as one argument to your batch file.)</p> + +<p>As a tutorial resource, have a look at <a href="../examples/test-data.lua.html#">test-data.lua</a> in the PL tests directory +for other examples of use, plus comments.</p> + +<p>The data returned by <a href="../libraries/pl.data.html#read">read</a> or constructed by <code>Data.copy_select</code> from a query is +basically just an array of rows: <code>{{1,2},{3,4}}</code>. So you may use <a href="../libraries/pl.data.html#read">read</a> to pull +in any array-like dataset, and process with any function that expects such a +implementation. In particular, the functions in <a href="../libraries/pl.array2d.html#">array2d</a> will work fine with +this data. In fact, these functions are available as methods; e.g. +<a href="../libraries/pl.array2d.html#flatten">array2d.flatten</a> can be called directly like so to give us a one-dimensional list:</p> + + +<pre> +v = data.read(<span class="string">'dat.txt'</span>):flatten() +</pre> + +<p>The data is also in exactly the right shape to be treated as matrices by +<a href="http://lua-users.org/wiki/LuaMatrix">LuaMatrix</a>:</p> + + +<pre> +> matrix = <span class="global">require</span> <span class="string">'matrix'</span> +> m = matrix(data.read <span class="string">'mat.txt'</span>) +> = m +<span class="number">1</span> <span class="number">0.2</span> <span class="number">0.3</span> +<span class="number">0.2</span> <span class="number">1</span> <span class="number">0.1</span> +<span class="number">0.1</span> <span class="number">0.2</span> <span class="number">1</span> +> = m^<span class="number">2</span> <span class="comment">-- same as m*m +</span><span class="number">1.07</span> <span class="number">0.46</span> <span class="number">0.62</span> +<span class="number">0.41</span> <span class="number">1.06</span> <span class="number">0.26</span> +<span class="number">0.24</span> <span class="number">0.42</span> <span class="number">1.05</span> +</pre> + +<p><a href="../libraries/pl.data.html#write">write</a> will write matrices back to files for you.</p> + +<p>Finally, for the curious, the global variable <code>_DEBUG</code> can be used to print out +the actual iterator function which a query generates and dynamically compiles. By +using code generation, we can get pretty much optimal performance out of +arbitrary queries.</p> + + +<pre> +> lua -lpl -e <span class="string">"_DEBUG=true"</span> -e <span class="string">"data.filter 'x,y where x > 4 sort by x'"</span> < test.txt +<span class="keyword">return</span> <span class="keyword">function</span> (t) + <span class="keyword">local</span> i = <span class="number">0</span> + <span class="keyword">local</span> v + <span class="keyword">local</span> ls = {} + <span class="keyword">for</span> i,v <span class="keyword">in</span> <span class="global">ipairs</span>(t) <span class="keyword">do</span> + <span class="keyword">if</span> v[<span class="number">1</span>] > <span class="number">4</span> <span class="keyword">then</span> + ls[#ls+<span class="number">1</span>] = v + <span class="keyword">end</span> + <span class="keyword">end</span> + <span class="global">table</span>.sort(ls,<span class="keyword">function</span>(v1,v2) + <span class="keyword">return</span> v1[<span class="number">1</span>] < v2[<span class="number">1</span>] + <span class="keyword">end</span>) + <span class="keyword">local</span> n = #ls + <span class="keyword">return</span> <span class="keyword">function</span>() + i = i + <span class="number">1</span> + v = ls[i] + <span class="keyword">if</span> i > n <span class="keyword">then</span> <span class="keyword">return</span> <span class="keyword">end</span> + <span class="keyword">return</span> v[<span class="number">1</span>],v[<span class="number">2</span>] + <span class="keyword">end</span> +<span class="keyword">end</span> + +<span class="number">10</span>,<span class="number">20</span> +<span class="number">40</span>,<span class="number">50</span> +</pre> + +<p><a name="Reading_Configuration_Files"></a></p> +<h3>Reading Configuration Files</h3> + +<p>The <a href="../libraries/pl.config.html#">config</a> module provides a simple way to convert several kinds of +configuration files into a Lua table. Consider the simple example:</p> + + +<pre> +# test.config +# Read timeout <span class="keyword">in</span> seconds +read.timeout=<span class="number">10</span> + +# Write timeout <span class="keyword">in</span> seconds +write.timeout=<span class="number">5</span> + +#acceptable ports +ports = <span class="number">1002</span>,<span class="number">1003</span>,<span class="number">1004</span> +</pre> + +<p>This can be easily brought in using <a href="../libraries/pl.config.html#read">config.read</a> and the result shown using +<a href="../libraries/pl.pretty.html#write">pretty.write</a>:</p> + + +<pre> +<span class="comment">-- readconfig.lua +</span><span class="keyword">local</span> config = <span class="global">require</span> <span class="string">'pl.config'</span> +<span class="keyword">local</span> pretty= <span class="global">require</span> <span class="string">'pl.pretty'</span> + +<span class="keyword">local</span> t = config.read(arg[<span class="number">1</span>]) +<span class="global">print</span>(pretty.write(t)) +</pre> + +<p>and the output of <code>lua readconfig.lua test.config</code> is:</p> + + +<pre> +{ + ports = { + <span class="number">1002</span>, + <span class="number">1003</span>, + <span class="number">1004</span> + }, + write_timeout = <span class="number">5</span>, + read_timeout = <span class="number">10</span> +} +</pre> + +<p>That is, <a href="../libraries/pl.config.html#read">config.read</a> will bring in all key/value pairs, ignore # comments, and +ensure that the key names are proper Lua identifiers by replacing non-identifier +characters with '_'. If the values are numbers, then they will be converted. (So +the value of <code>t.write_timeout</code> is the number 5). In addition, any values which +are separated by commas will be converted likewise into an array.</p> + +<p>Any line can be continued with a backslash. So this will all be considered one +line:</p> + + +<pre> +names=one,two,three, \ +four,five,six,seven, \ +eight,nine,ten +</pre> + +<p>Windows-style INI files are also supported. The section structure of INI files +translates naturally to nested tables in Lua:</p> + + +<pre> +; test.ini +[timeouts] +read=<span class="number">10</span> ; Read timeout <span class="keyword">in</span> seconds +write=<span class="number">5</span> ; Write timeout <span class="keyword">in</span> seconds +[portinfo] +ports = <span class="number">1002</span>,<span class="number">1003</span>,<span class="number">1004</span> +</pre> + +<p> The output is:</p> + + +<pre> +{ + portinfo = { + ports = { + <span class="number">1002</span>, + <span class="number">1003</span>, + <span class="number">1004</span> + } + }, + timeouts = { + write = <span class="number">5</span>, + read = <span class="number">10</span> + } +} +</pre> + +<p>You can now refer to the write timeout as <code>t.timeouts.write</code>.</p> + +<p>As a final example of the flexibility of <a href="../libraries/pl.config.html#read">config.read</a>, if passed this simple +comma-delimited file</p> + + +<pre> +one,two,three +<span class="number">10</span>,<span class="number">20</span>,<span class="number">30</span> +<span class="number">40</span>,<span class="number">50</span>,<span class="number">60</span> +<span class="number">1</span>,<span class="number">2</span>,<span class="number">3</span> +</pre> + +<p>it will produce the following table:</p> + + +<pre> +{ + { <span class="string">"one"</span>, <span class="string">"two"</span>, <span class="string">"three"</span> }, + { <span class="number">10</span>, <span class="number">20</span>, <span class="number">30</span> }, + { <span class="number">40</span>, <span class="number">50</span>, <span class="number">60</span> }, + { <span class="number">1</span>, <span class="number">2</span>, <span class="number">3</span> } +} +</pre> + +<p><a href="../libraries/pl.config.html#read">config.read</a> isn't designed to read all CSV files in general, but intended to +support some Unix configuration files not structured as key-value pairs, such as +'/etc/passwd'.</p> + +<p>This function is intended to be a Swiss Army Knife of configuration readers, but +it does have to make assumptions, and you may not like them. So there is an +optional extra parameter which allows some control, which is table that may have +the following fields:</p> + + +<pre> +{ + variablilize = <span class="keyword">true</span>, + convert_numbers = <span class="global">tonumber</span>, + trim_space = <span class="keyword">true</span>, + list_delim = <span class="string">','</span>, + trim_quotes = <span class="keyword">true</span>, + ignore_assign = <span class="keyword">false</span>, + keysep = <span class="string">'='</span>, + smart = <span class="keyword">false</span>, +} +</pre> + +<p><code>variablilize</code> is the option that converted <code>write.timeout</code> in the first example +to the valid Lua identifier <code>write_timeout</code>. If <code>convert_numbers</code> is true, then +an attempt is made to convert any string that starts like a number. You can +specify your own function (say one that will convert a string like '5224 kb' into +a number.)</p> + +<p><code>trim_space</code> ensures that there is no starting or trailing whitespace with +values, and <code>list_delim</code> is the character that will be used to decide whether to +split a value up into a list (it may be a Lua string pattern such as '%s+'.)</p> + +<p>For instance, the password file in Unix is colon-delimited:</p> + + +<pre> +t = config.read(<span class="string">'/etc/passwd'</span>,{list_delim=<span class="string">':'</span>}) +</pre> + +<p>This produces the following output on my system (only last two lines shown):</p> + + +<pre> +{ + ... + { + <span class="string">"user"</span>, + <span class="string">"x"</span>, + <span class="string">"1000"</span>, + <span class="string">"1000"</span>, + <span class="string">"user,,,"</span>, + <span class="string">"/home/user"</span>, + <span class="string">"/bin/bash"</span> + }, + { + <span class="string">"sdonovan"</span>, + <span class="string">"x"</span>, + <span class="string">"1001"</span>, + <span class="string">"1001"</span>, + <span class="string">"steve donovan,28,,"</span>, + <span class="string">"/home/sdonovan"</span>, + <span class="string">"/bin/bash"</span> + } +} +</pre> + +<p>You can get this into a more sensible format, where the usernames are the keys, +with this (the <a href="../libraries/pl.tablex.html#pairmap">tablex.pairmap</a> function must return value, key!)</p> + + +<pre> +t = tablex.pairmap(<span class="keyword">function</span>(k,v) <span class="keyword">return</span> v,v[<span class="number">1</span>] <span class="keyword">end</span>,t) +</pre> + +<p>and you get:</p> + + +<pre> +{ ... + sdonovan = { + <span class="string">"sdonovan"</span>, + <span class="string">"x"</span>, + <span class="string">"1001"</span>, + <span class="string">"1001"</span>, + <span class="string">"steve donovan,28,,"</span>, + <span class="string">"/home/sdonovan"</span>, + <span class="string">"/bin/bash"</span> + } +... +} +</pre> + +<p>Many common Unix configuration files can be read by tweaking these parameters. +For <code>/etc/fstab</code>, the options <code>{list_delim='%s+',ignore_assign=true}</code> will +correctly separate the columns. It's common to find 'KEY VALUE' assignments in +files such as <code>/etc/ssh/ssh_config</code>; the options <code>{keysep=' '}</code> make +<a href="../libraries/pl.config.html#read">config.read</a> return a table where each KEY has a value VALUE.</p> + +<p>Files in the Linux <code>procfs</code> usually use ':` as the field delimiter:</p> + + +<pre> +> t = config.read(<span class="string">'/proc/meminfo'</span>,{keysep=<span class="string">':'</span>}) +> = t.MemFree +<span class="number">220140</span> kB +</pre> + +<p>That result is a string, since <a href="https://www.lua.org/manual/5.1/manual.html#pdf-tonumber">tonumber</a> doesn't like it, but defining the +<code>convert_numbers</code> option as `function(s) return tonumber((s:gsub(' kB$',''))) +end` will get the memory figures as actual numbers in the result. (The extra +parentheses are necessary so that <a href="https://www.lua.org/manual/5.1/manual.html#pdf-tonumber">tonumber</a> only gets the first result from +<code>gsub</code>). From `tests/test-config.lua':</p> + + +<pre> +testconfig(<span class="string">[[ +MemTotal: 1024748 kB +MemFree: 220292 kB +]]</span>, +{ MemTotal = <span class="number">1024748</span>, MemFree = <span class="number">220292</span> }, +{ + keysep = <span class="string">':'</span>, + convert_numbers = <span class="keyword">function</span>(s) + s = s:gsub(<span class="string">' kB$'</span>,<span class="string">''</span>) + <span class="keyword">return</span> <span class="global">tonumber</span>(s) + <span class="keyword">end</span> + } +) +</pre> + +<p>The <code>smart</code> option lets <a href="../libraries/pl.config.html#read">config.read</a> make a reasonable guess for you; there +are examples in <code>tests/test-config.lua</code>, but basically these common file +formats (and those following the same pattern) can be processed directly in +smart mode: 'etc/fstab', '/proc/XXXX/status', 'ssh_config' and 'pdatedb.conf'.</p> + +<p>Please note that <a href="../libraries/pl.config.html#read">config.read</a> can be passed a <em>file-like object</em>; if it's not a +string and supports the <a href="../libraries/pl.data.html#read">read</a> method, then that will be used. For instance, to +read a configuration from a string, use <a href="../libraries/pl.stringio.html#open">stringio.open</a>.</p> + + +<p><a id="lexer"/></p> + +<p><a name="Lexical_Scanning"></a></p> +<h3>Lexical Scanning</h3> + +<p>Although Lua's string pattern matching is very powerful, there are times when +something more powerful is needed. <a href="../libraries/pl.lexer.html#scan">pl.lexer.scan</a> provides lexical scanners +which <em>tokenize</em> a string, classifying tokens into numbers, strings, etc.</p> + + +<pre> +> lua -lpl +Lua <span class="number">5.1</span>.<span class="number">4</span> Copyright (C) <span class="number">1994</span>-<span class="number">2008</span> Lua.org, PUC-Rio +> tok = lexer.scan <span class="string">'alpha = sin(1.5)'</span> +> = tok() +iden alpha +> = tok() += = +> = tok() +iden sin +> = tok() +( ( +> = tok() +number <span class="number">1.5</span> +> = tok() +) ) +> = tok() +(<span class="keyword">nil</span>) +</pre> + +<p>The scanner is a function, which is repeatedly called and returns the <em>type</em> and +<em>value</em> of the token. Recognized basic types are 'iden','string','number', and +'space'. and everything else is represented by itself. Note that by default the +scanner will skip any 'space' tokens.</p> + +<p>'comment' and 'keyword' aren't applicable to the plain scanner, which is not +language-specific, but a scanner which understands Lua is available. It +recognizes the Lua keywords, and understands both short and long comments and +strings.</p> + + +<pre> +> <span class="keyword">for</span> t,v <span class="keyword">in</span> lexer.lua <span class="string">'for i=1,n do'</span> <span class="keyword">do</span> <span class="global">print</span>(t,v) <span class="keyword">end</span> +keyword <span class="keyword">for</span> +iden i += = +number <span class="number">1</span> +, , +iden n +keyword <span class="keyword">do</span> +</pre> + +<p>A lexical scanner is useful where you have highly-structured data which is not +nicely delimited by newlines. For example, here is a snippet of a in-house file +format which it was my task to maintain:</p> + + +<pre> +points + (<span class="number">818344.1</span>,-<span class="number">20389.7</span>,-<span class="number">0.1</span>),(<span class="number">818337.9</span>,-<span class="number">20389.3</span>,-<span class="number">0.1</span>),(<span class="number">818332.5</span>,-<span class="number">20387.8</span>,-<span class="number">0.1</span>) + ,(<span class="number">818327.4</span>,-<span class="number">20388</span>,-<span class="number">0.1</span>),(<span class="number">818322</span>,-<span class="number">20387.7</span>,-<span class="number">0.1</span>),(<span class="number">818316.3</span>,-<span class="number">20388.6</span>,-<span class="number">0.1</span>) + ,(<span class="number">818309.7</span>,-<span class="number">20389.4</span>,-<span class="number">0.1</span>),(<span class="number">818303.5</span>,-<span class="number">20390.6</span>,-<span class="number">0.1</span>),(<span class="number">818295.8</span>,-<span class="number">20388.3</span>,-<span class="number">0.1</span>) + ,(<span class="number">818290.5</span>,-<span class="number">20386.9</span>,-<span class="number">0.1</span>),(<span class="number">818285.2</span>,-<span class="number">20386.1</span>,-<span class="number">0.1</span>),(<span class="number">818279.3</span>,-<span class="number">20383.6</span>,-<span class="number">0.1</span>) + ,(<span class="number">818274</span>,-<span class="number">20381.2</span>,-<span class="number">0.1</span>),(<span class="number">818274</span>,-<span class="number">20380.7</span>,-<span class="number">0.1</span>); +</pre> + +<p>Here is code to extract the points using <a href="../libraries/pl.lexer.html#">pl.lexer</a>:</p> + + +<pre> +<span class="comment">-- assume 's' contains the text above... +</span><span class="keyword">local</span> lexer = <span class="global">require</span> <span class="string">'pl.lexer'</span> +<span class="keyword">local</span> expecting = lexer.expecting +<span class="keyword">local</span> append = <span class="global">table</span>.insert + +<span class="keyword">local</span> tok = lexer.scan(s) + +<span class="keyword">local</span> points = {} +<span class="keyword">local</span> t,v = tok() <span class="comment">-- should be 'iden','points' +</span> +<span class="keyword">while</span> t ~= <span class="string">';'</span> <span class="keyword">do</span> + c = {} + expecting(tok,<span class="string">'('</span>) + c.x = expecting(tok,<span class="string">'number'</span>) + expecting(tok,<span class="string">','</span>) + c.y = expecting(tok,<span class="string">'number'</span>) + expecting(tok,<span class="string">','</span>) + c.z = expecting(tok,<span class="string">'number'</span>) + expecting(tok,<span class="string">')'</span>) + t,v = tok() <span class="comment">-- either ',' or ';' +</span> append(points,c) +<span class="keyword">end</span> +</pre> + +<p>The <code>expecting</code> function grabs the next token and if the type doesn't match, it +throws an error. (<a href="../libraries/pl.lexer.html#">pl.lexer</a>, unlike other PL libraries, raises errors if +something goes wrong, so you should wrap your code in <a href="https://www.lua.org/manual/5.1/manual.html#pdf-pcall">pcall</a> to catch the error +gracefully.)</p> + +<p>The scanners all have a second optional argument, which is a table which controls +whether you want to exclude spaces and/or comments. The default for <a href="../libraries/pl.lexer.html#lua">lexer.lua</a> +is <code>{space=true,comments=true}</code>. There is a third optional argument which +determines how string and number tokens are to be processsed.</p> + +<p>The ultimate highly-structured data is of course, program source. Here is a +snippet from 'text-lexer.lua':</p> + + +<pre> +<span class="global">require</span> <span class="string">'pl'</span> + +lines = <span class="string">[[ +for k,v in pairs(t) do + if type(k) == 'number' then + print(v) -- array-like case + else + print(k,v) + end +end +]]</span> + +ls = List() +<span class="keyword">for</span> tp,val <span class="keyword">in</span> lexer.lua(lines,{space=<span class="keyword">true</span>,comments=<span class="keyword">true</span>}) <span class="keyword">do</span> + <span class="global">assert</span>(tp ~= <span class="string">'space'</span> <span class="keyword">and</span> tp ~= <span class="string">'comment'</span>) + <span class="keyword">if</span> tp == <span class="string">'keyword'</span> <span class="keyword">then</span> ls:append(val) <span class="keyword">end</span> +<span class="keyword">end</span> +test.asserteq(ls,List{<span class="string">'for'</span>,<span class="string">'in'</span>,<span class="string">'do'</span>,<span class="string">'if'</span>,<span class="string">'then'</span>,<span class="string">'else'</span>,<span class="string">'end'</span>,<span class="string">'end'</span>}) +</pre> + +<p>Here is a useful little utility that identifies all common global variables found +in a lua module (ignoring those declared locally for the moment):</p> + + +<pre> +<span class="comment">-- testglobal.lua +</span><span class="global">require</span> <span class="string">'pl'</span> + +<span class="keyword">local</span> txt,err = utils.readfile(arg[<span class="number">1</span>]) +<span class="keyword">if</span> <span class="keyword">not</span> txt <span class="keyword">then</span> <span class="keyword">return</span> <span class="global">print</span>(err) <span class="keyword">end</span> + +<span class="keyword">local</span> globals = List() +<span class="keyword">for</span> t,v <span class="keyword">in</span> lexer.lua(txt) <span class="keyword">do</span> + <span class="keyword">if</span> t == <span class="string">'iden'</span> <span class="keyword">and</span> _G[v] <span class="keyword">then</span> + globals:append(v) + <span class="keyword">end</span> +<span class="keyword">end</span> +pretty.dump(seq.count_map(globals)) +</pre> + +<p>Rather then dumping the whole list, with its duplicates, we pass it through +<a href="../libraries/pl.seq.html#count_map">seq.count_map</a> which turns the list into a table where the keys are the values, +and the associated values are the number of times those values occur in the +sequence. Typical output looks like this:</p> + + +<pre> +{ + <span class="global">type</span> = <span class="number">2</span>, + <span class="global">pairs</span> = <span class="number">2</span>, + <span class="global">table</span> = <span class="number">2</span>, + <span class="global">print</span> = <span class="number">3</span>, + <span class="global">tostring</span> = <span class="number">2</span>, + <span class="global">require</span> = <span class="number">1</span>, + <span class="global">ipairs</span> = <span class="number">4</span> +} +</pre> + +<p>You could further pass this through <a href="../libraries/pl.tablex.html#keys">tablex.keys</a> to get a unique list of +symbols. This can be useful when writing 'strict' Lua modules, where all global +symbols must be defined as locals at the top of the file.</p> + +<p>For a more detailed use of <a href="../libraries/pl.lexer.html#scan">lexer.scan</a>, please look at <a href="../examples/testxml.lua.html#">testxml.lua</a> in the +examples directory.</p> + +<p><a name="XML"></a></p> +<h3>XML</h3> + +<p>New in the 0.9.7 release is some support for XML. This is a large topic, and +Penlight does not provide a full XML stack, which is properly the task of a more +specialized library.</p> + +<h4>Parsing and Pretty-Printing</h4> + +<p>The semi-standard XML parser in the Lua universe is <a href="http://matthewwild.co.uk/projects/luaexpat/">lua-expat</a>. +In particular, +it has a function called <code>lxp.lom.parse</code> which will parse XML into the Lua Object +Model (LOM) format. However, it does not provide a way to convert this data back +into XML text. <a href="../libraries/pl.xml.html#parse">xml.parse</a> will use this function, <em>if</em> <code>lua-expat</code> is +available, and otherwise switches back to a pure Lua parser originally written by +Roberto Ierusalimschy.</p> + +<p>The resulting document object knows how to render itself as a string, which is +useful for debugging:</p> + + +<pre> +> d = xml.parse <span class="string">"<nodes><node id='1'>alice</node></nodes>"</span> +> = d +<nodes><node id=<span class="string">'1'</span>>alice</node></nodes> +> pretty.dump (d) +{ + { + <span class="string">"alice"</span>, + attr = { + <span class="string">"id"</span>, + id = <span class="string">"1"</span> + }, + tag = <span class="string">"node"</span> + }, + attr = { + }, + tag = <span class="string">"nodes"</span> +} +</pre> + +<p>Looking at the actual shape of the data reveals the structure of LOM:</p> + +<ul> + <li>every element has a <code>tag</code> field with its name</li> + <li>plus a <code>attr</code> field which is a table containing the attributes as fields, and + also as an array. It is always present.</li> + <li>the children of the element are the array part of the element, so <code>d[1]</code> is + the first child of <code>d</code>, etc.</li> +</ul> + +<p>It could be argued that having attributes also as the array part of <code>attr</code> is not +essential (you cannot depend on attribute order in XML) but that's how +it goes with this standard.</p> + +<p><code>lua-expat</code> is another <em>soft dependency</em> of Penlight; generally, the fallback +parser is good enough for straightforward XML as is commonly found in +configuration files, etc. <code>doc.basic_parse</code> is not intended to be a proper +conforming parser (it's only sixty lines) but it handles simple kinds of +documents that do not have comments or DTD directives. It is intelligent enough +to ignore the <code><?xml</code> directive and that is about it.</p> + +<p>You can get pretty-printing by explicitly calling <a href="../libraries/pl.xml.html#tostring">xml.tostring</a> and passing it +the initial indent and the per-element indent:</p> + + +<pre> +> = xml.<span class="global">tostring</span>(d,<span class="string">''</span>,<span class="string">' '</span>) + +<nodes> + <node id=<span class="string">'1'</span>>alice</node> +</nodes> +</pre> + +<p>There is a fourth argument which is the <em>attribute indent</em>:</p> + + +<pre> +> a = xml.parse <span class="string">"<frodo name='baggins' age='50' type='hobbit'/>"</span> +> = xml.<span class="global">tostring</span>(a,<span class="string">''</span>,<span class="string">' '</span>,<span class="string">' '</span>) + +<frodo + <span class="global">type</span>=<span class="string">'hobbit'</span> + name=<span class="string">'baggins'</span> + age=<span class="string">'50'</span> +/> +</pre> + +<h4>Parsing and Working with Configuration Files</h4> + +<p>It's common to find configurations expressed with XML these days. It's +straightforward to 'walk' the <a href="http://matthewwild.co.uk/projects/luaexpat/lom.html">LOM</a> +data and extract the data in the form you want:</p> + + +<pre> +<span class="global">require</span> <span class="string">'pl'</span> + +<span class="keyword">local</span> config = <span class="string">[[ +<config> + <alpha>1.3</alpha> + <beta>10</beta> + <name>bozo</name> +</config> +]]</span> +<span class="keyword">local</span> d,err = xml.parse(config) + +<span class="keyword">local</span> t = {} +<span class="keyword">for</span> item <span class="keyword">in</span> d:childtags() <span class="keyword">do</span> + t[item.tag] = item[<span class="number">1</span>] +<span class="keyword">end</span> + +pretty.dump(t) +<span class="comment">---> +</span>{ + beta = <span class="string">"10"</span>, + alpha = <span class="string">"1.3"</span>, + name = <span class="string">"bozo"</span> +} +</pre> + +<p>The only gotcha is that here we must use the <code>Doc:childtags</code> method, which will +skip over any text elements.</p> + +<p>A more involved example is this excerpt from <code>serviceproviders.xml</code>, which is +usually found at <code>/usr/share/mobile-broadband-provider-info/serviceproviders.xml</code> +on Debian/Ubuntu Linux systems.</p> + + +<pre> +d = xml.parse <span class="string">[[ +<serviceproviders format="2.0"> +... +<country code="za"> + <provider> + <name>Cell-c</name> + <gsm> + <network-id mcc="655" mnc="07"/> + <apn value="internet"> + <username>Cellcis</username> + <dns>196.7.0.138</dns> + <dns>196.7.142.132</dns> + </apn> + </gsm> + </provider> + <provider> + <name>MTN</name> + <gsm> + <network-id mcc="655" mnc="10"/> + <apn value="internet"> + <dns>196.11.240.241</dns> + <dns>209.212.97.1</dns> + </apn> + </gsm> + </provider> + <provider> + <name>Vodacom</name> + <gsm> + <network-id mcc="655" mnc="01"/> + <apn value="internet"> + <dns>196.207.40.165</dns> + <dns>196.43.46.190</dns> + </apn> + <apn value="unrestricted"> + <name>Unrestricted</name> + <dns>196.207.32.69</dns> + <dns>196.43.45.190</dns> + </apn> + </gsm> + </provider> + <provider> + <name>Virgin Mobile</name> + <gsm> + <apn value="vdata"> + <dns>196.7.0.138</dns> + <dns>196.7.142.132</dns> + </apn> + </gsm> + </provider> +</country> +.... +</serviceproviders> +]]</span> +</pre> + +<p>Getting the names of the providers per-country is straightforward:</p> + + +<pre> +<span class="keyword">local</span> t = {} +<span class="keyword">for</span> country <span class="keyword">in</span> d:childtags() <span class="keyword">do</span> + <span class="keyword">local</span> providers = {} + t[country.attr.code] = providers + <span class="keyword">for</span> provider <span class="keyword">in</span> country:childtags() <span class="keyword">do</span> + <span class="global">table</span>.insert(providers,provider:child_with_name(<span class="string">'name'</span>):get_text()) + <span class="keyword">end</span> +<span class="keyword">end</span> + +pretty.dump(t) +<span class="comment">--> +</span>{ + za = { + <span class="string">"Cell-c"</span>, + <span class="string">"MTN"</span>, + <span class="string">"Vodacom"</span>, + <span class="string">"Virgin Mobile"</span> + } + .... +} +</pre> + +<h4>Generating XML with 'xmlification'</h4> + +<p>This feature is inspired by the <code>htmlify</code> function used by +<a href="http://keplerproject.github.com/orbit/">Orbit</a> to simplify HTML generation, +except that no function environment magic is used; the <code>tags</code> function returns a +set of <em>constructors</em> for elements of the given tag names.</p> + + +<pre> +> nodes, node = xml.tags <span class="string">'nodes, node'</span> +> = node <span class="string">'alice'</span> +<node>alice</node> +> = nodes { node {id=<span class="string">'1'</span>,<span class="string">'alice'</span>}} +<nodes><node id=<span class="string">'1'</span>>alice</node></nodes> +</pre> + +<p>The flexibility of Lua tables is very useful here, since both the attributes and +the children of an element can be encoded naturally. The argument to these tag +constructors is either a single value (like a string) or a table where the +attributes are the named keys and the children are the array values.</p> + +<h4>Generating XML using Templates</h4> + +<p>A template is a little XML document which contains dollar-variables. The <code>subst</code> +method on a document is fed an array of tables containing values for these +variables. Note how the parent tag name is specified:</p> + + +<pre> +> templ = xml.parse <span class="string">"<node id='$id'>$name</node>"</span> +> = templ:subst {tag=<span class="string">'nodes'</span>, {id=<span class="number">1</span>,name=<span class="string">'alice'</span>},{id=<span class="number">2</span>,name=<span class="string">'john'</span>}} +<nodes><node id=<span class="string">'1'</span>>alice</node><node id=<span class="string">'2'</span>>john</node></nodes> +</pre> + +<p>Substitution is very related to <em>filtering</em> documents. One of the annoying things +about XML is that it is a document markup language first, and a data language +second. Standard parsers will assume you really care about all those extra +text elements. Consider this fragment, which has been changed by a five-year old:</p> + + +<pre> +T = <span class="string">[[ + <weather> + boops! + <current_conditions> + <condition data='$condition'/> + <temp_c data='$temp'/> + <bo>whoops!</bo> + </current_conditions> + </weather> +]]</span> +</pre> + +<p>Conformant parsers will give you text elements with the line feed after <code><current_conditions></code> +although it makes handling the data more irritating.</p> + + +<pre> +<span class="keyword">local</span> <span class="keyword">function</span> parse (str) + <span class="keyword">return</span> xml.parse(str,<span class="keyword">false</span>,<span class="keyword">true</span>) +<span class="keyword">end</span> +</pre> + +<p>Second argument means 'string, not file' and third argument means use the built-in +Lua parser (instead of LuaExpat if available) which <em>by default</em> is not interested in +keeping such strings.</p> + +<p>How to remove the string <code>boops!</code>? <code>clone</code> (also called <a href="../libraries/pl.data.html#filter">filter</a> when called as a +method) copies a LOM document. It can be passed a filter function, which is applied +to each string found. The powerful thing about this is that this function receives +structural information - the parent node, and whether this was a tag name, a text +element or a attribute name:</p> + + +<pre> +d = parse (T) +c = d:filter(<span class="keyword">function</span>(s,kind,parent) + <span class="global">print</span>(stringx.strip(s),kind,parent <span class="keyword">and</span> parent.tag <span class="keyword">or</span> <span class="string">'?'</span>) + <span class="keyword">if</span> kind == <span class="string">'*TEXT'</span> <span class="keyword">and</span> #parent > <span class="number">1</span> <span class="keyword">then</span> <span class="keyword">return</span> <span class="keyword">nil</span> <span class="keyword">end</span> + <span class="keyword">return</span> s +<span class="keyword">end</span>) +<span class="comment">---> +</span>weather *TAG ? +boops! *TEXT weather +current_conditions *TAG weather +condition *TAG current_conditions +$condition data condition +temp_c *TAG current_conditions +$temp data temp_c +bo *TAG current_conditions +whoops! *TEXT bo +</pre> + +<p>We can pull out 'boops' and not 'whoops' by discarding text elements which are not +the single child of an element.</p> + + + +<h4>Extracting Data using Templates</h4> + +<p>Matching goes in the opposite direction. We have a document, and would like to +extract values from it using a pattern.</p> + +<p>A common use of this is parsing the XML result of API queries. The +<a href="http://blog.programmableweb.com/2010/02/08/googles-secret-weather-api/">(undocumented and subsequently discontinued) Google Weather +API</a> is a +good example. Grabbing the result of +`http://www.google.com/ig/api?weather=Johannesburg,ZA" we get something like +this, after pretty-printing:</p> + + +<pre> +<xml_api_reply version=<span class="string">'1'</span>> + <weather module_id=<span class="string">'0'</span> tab_id=<span class="string">'0'</span> mobile_zipped=<span class="string">'1'</span> section=<span class="string">'0'</span> row=<span class="string">'0'</span> +</pre> + +<p>mobile_row='0'></p> + +<pre> +<forecast_information> + <city data=<span class="string">'Johannesburg, Gauteng'</span>/> + <postal_code data=<span class="string">'Johannesburg,ZA'</span>/> + <latitude_e6 data=<span class="string">''</span>/> + <longitude_e6 data=<span class="string">''</span>/> + <forecast_date data=<span class="string">'2010-10-02'</span>/> + <current_date_time data=<span class="string">'2010-10-02 18:30:00 +0000'</span>/> + <unit_system data=<span class="string">'US'</span>/> +</forecast_information> +<current_conditions> + <condition data=<span class="string">'Clear'</span>/> + <temp_f data=<span class="string">'75'</span>/> + <temp_c data=<span class="string">'24'</span>/> + <humidity data=<span class="string">'Humidity: 19%'</span>/> + <icon data=<span class="string">'/ig/images/weather/sunny.gif'</span>/> + <wind_condition data=<span class="string">'Wind: NW at 7 mph'</span>/> +</current_conditions> +<forecast_conditions> + <day_of_week data=<span class="string">'Sat'</span>/> + <low data=<span class="string">'60'</span>/> + <high data=<span class="string">'89'</span>/> + <icon data=<span class="string">'/ig/images/weather/sunny.gif'</span>/> + <condition data=<span class="string">'Clear'</span>/> +</forecast_conditions> +.... +/weather> +l_api_reply> +</pre> + +<p>Assume that the above XML has been read into <code>google</code>. The idea is to write a +pattern looking like a template, and use it to extract some values of interest:</p> + + +<pre> +t = <span class="string">[[ + <weather> + <current_conditions> + <condition data='$condition'/> + <temp_c data='$temp'/> + </current_conditions> + </weather> +]]</span> + +<span class="keyword">local</span> res, ret = google:match(t) +pretty.dump(res) +</pre> + +<p>And the output is:</p> + + +<pre> +{ + condition = <span class="string">"Clear"</span>, + temp = <span class="string">"24"</span> +} +</pre> + +<p>The <code>match</code> method can be passed a LOM document or some text, which will be +parsed first.</p> + +<p>But what if we need to extract values from repeated elements? Match templates may +contain 'array matches' which are enclosed in '{{..}}':</p> + + +<pre> +<weather> + {{<forecast_conditions> + <day_of_week data=<span class="string">'$day'</span>/> + <low data=<span class="string">'$low'</span>/> + <high data=<span class="string">'$high'</span>/> + <condition data=<span class="string">'$condition'</span>/> + </forecast_conditions>}} +</weather> +</pre> + +<p>And the match result is:</p> + + +<pre> +{ + { + low = <span class="string">"60"</span>, + high = <span class="string">"89"</span>, + day = <span class="string">"Sat"</span>, + condition = <span class="string">"Clear"</span>, + }, + { + low = <span class="string">"53"</span>, + high = <span class="string">"86"</span>, + day = <span class="string">"Sun"</span>, + condition = <span class="string">"Clear"</span>, + }, + { + low = <span class="string">"57"</span>, + high = <span class="string">"87"</span>, + day = <span class="string">"Mon"</span>, + condition = <span class="string">"Clear"</span>, + }, + { + low = <span class="string">"60"</span>, + high = <span class="string">"84"</span>, + day = <span class="string">"Tue"</span>, + condition = <span class="string">"Clear"</span>, + } +} +</pre> + +<p>With this array of tables, you can use <a href="../libraries/pl.tablex.html#">tablex</a> or <a href="../classes/pl.List.html#">List</a> +to reshape into the desired form, if you choose. Just as with reading a Unix password +file with <a href="../libraries/pl.config.html#">config</a>, you can make the array into a map of days to conditions using:</p> + + +<pre> +<span class="backtick"><a href="../libraries/pl.tablex.html#pairmap">tablex.pairmap</a></span>(<span class="string">'|k,v| v,v.day'</span>,conditions) +</pre> + +<p>(Here using the alternative string lambda option)</p> + +<p>However, xml matches can shape the structure of the output. By replacing the <code>day_of_week</code> +line of the template with <code><day_of_week data='$_'/></code> we get the same effect; <code>$_</code> is +a special symbol that means that this captured value (or simply <em>capture</em>) becomes the key.</p> + +<p>Note that <code>$NUMBER</code> means a numerical index, so +that <code>$1</code> is the first element of the resulting array, and so forth. You can mix +numbered and named captures, but it's strongly advised to make the numbered captures +form a proper array sequence (everything from <code>1</code> to <code>n</code> inclusive). <code>$0</code> has a +special meaning; if it is the only capture (<code>{[0]='foo'}</code>) then the table is +collapsed into 'foo'.</p> + + +<pre> +<weather> + {{<forecast_conditions> + <day_of_week data=<span class="string">'$_'</span>/> + <low data=<span class="string">'$1'</span>/> + <high data=<span class="string">'$2'</span>/> + <condition data=<span class="string">'$3'</span>/> + </forecast_conditions>}} +</weather> +</pre> + +<p>Now the result is:</p> + + +<pre> +{ + Tue = { + <span class="string">"60"</span>, + <span class="string">"84"</span>, + <span class="string">"Clear"</span> + }, + Sun = { + <span class="string">"53"</span>, + <span class="string">"86"</span>, + <span class="string">"Clear"</span> + }, + Sat = { + <span class="string">"60"</span>, + <span class="string">"89"</span>, + <span class="string">"Clear"</span> + }, + Mon = { + <span class="string">"57"</span>, + <span class="string">"87"</span>, + <span class="string">"Clear"</span> + } +} +</pre> + +<p>Applying matches to this config file poses another problem, because the actual +tags matched are themselves meaningful.</p> + + +<pre> +<config> + <alpha><span class="number">1.3</span></alpha> + <beta><span class="number">10</span></beta> + <name>bozo</name> +</config> +</pre> + +<p>So there are tag 'wildcards' which are element names ending with a hyphen.</p> + + +<pre> +<config> + {{<key->$value</key->}} +</config> +</pre> + +<p>You will then get <code>{{alpha='1.3'},...}</code>. The most convenient format would be +returned by this (note that <code>_-</code> behaves just like <code>$_</code>):</p> + + +<pre> +<config> + {{<_->$<span class="number">0</span></_->}} +</config> +</pre> + +<p>which would return <code>{alpha='1.3',beta='10',name='bozo'}</code>.</p> + +<p>We could play this game endlessly, and encode ways of converting captures, but +the scheme is complex enough, and it's easy to do the conversion later</p> + + +<pre> +<span class="keyword">local</span> numbers = {alpha=<span class="keyword">true</span>,beta=<span class="keyword">true</span>} +<span class="keyword">for</span> k,v <span class="keyword">in</span> <span class="global">pairs</span>(res) <span class="keyword">do</span> + <span class="keyword">if</span> numbers[v] <span class="keyword">then</span> res[k] = <span class="global">tonumber</span>(v) <span class="keyword">end</span> +<span class="keyword">end</span> +</pre> + +<h4>HTML Parsing</h4> + +<p>HTML is an unusually degenerate form of XML, and Dennis Schridde has contributed +a feature which makes parsing it easier. For instance, from the tests:</p> + + +<pre> +doc = xml.parsehtml <span class="string">[[ +<BODY> +Hello dolly<br> +HTML is <b>slack</b><br> +</BODY> +]]</span> + +asserteq(xml.<span class="global">tostring</span>(doc),<span class="string">[[ +<body> +Hello dolly<br/> +HTML is <b>slack</b><br/></body>]]</span>) +</pre> + +<p>That is, all tags are converted to lowercase, and empty HTML elements like <code>br</code> +are properly closed; attributes do not need to be quoted.</p> + +<p>Also, DOCTYPE directives and comments are skipped. For truly badly formed HTML, +this is not the tool for you!</p> + + + + + +</div> <!-- id="content" --> +</div> <!-- id="main" --> +<div id="about"> +<i>generated by <a href="http://github.com/stevedonovan/LDoc">LDoc 1.4.6</a></i> +</div> <!-- id="about" --> +</div> <!-- id="container" --> +</body> +</html> |