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<!DOCTYPE html>
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<title>Filtering — Lua Functional 0.1.3 documentation</title>
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<div class="header" role="banner"><img class="rightlogo" src="_static/logo.png" alt="Logo"/><h1 class="heading"><a href="index.html">
<span>Lua Functional 0.1.3 documentation</span></a></h1>
<h2 class="heading"><span>Filtering</span></h2>
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<div class="content" role="main">
<section id="filtering">
<h1>Filtering<a class="headerlink" href="#filtering" title="Permalink to this headline">¶</a></h1>
<p>This section contains functions to filter values during iteration.</p>
<dl class="py function">
<dt class="sig sig-object py" id="fun.filter">
<span class="sig-prename descclassname"><span class="pre">fun.</span></span><span class="sig-name descname"><span class="pre">filter</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">predicate</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">gen</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">param</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">state</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#fun.filter" title="Permalink to this definition">¶</a></dt>
<dt class="sig sig-object py">
<span class="sig-name descname"><span class="pre">iterator:filter(predicate)</span></span></dt>
<dd><dl class="field-list simple">
<dt class="field-odd">Parameters</dt>
<dd class="field-odd"><p><strong>param</strong> (<em>(</em><em>function</em><em>(</em><em>...</em><em>) </em><em>-> bool</em><em>)</em>) – an predicate to filter the iterator</p>
</dd>
</dl>
<p>Return a new iterator of those elements that satisfy the <strong>predicate</strong>.</p>
<p>Examples:</p>
<div class="highlight-lua notranslate"><div class="highlight"><pre><span></span><span class="o">></span> <span class="n">each</span><span class="p">(</span><span class="nb">print</span><span class="p">,</span> <span class="n">filter</span><span class="p">(</span><span class="kr">function</span><span class="p">(</span><span class="n">x</span><span class="p">)</span> <span class="kr">return</span> <span class="n">x</span> <span class="o">%</span> <span class="mi">3</span> <span class="o">==</span> <span class="mi">0</span> <span class="kr">end</span><span class="p">,</span> <span class="n">range</span><span class="p">(</span><span class="mi">10</span><span class="p">)))</span>
<span class="mi">3</span>
<span class="mi">6</span>
<span class="mi">9</span>
<span class="o">></span> <span class="n">each</span><span class="p">(</span><span class="nb">print</span><span class="p">,</span> <span class="n">take</span><span class="p">(</span><span class="mi">5</span><span class="p">,</span> <span class="n">filter</span><span class="p">(</span><span class="kr">function</span><span class="p">(</span><span class="n">i</span><span class="p">,</span> <span class="n">x</span><span class="p">)</span> <span class="kr">return</span> <span class="n">i</span> <span class="o">%</span> <span class="mi">3</span> <span class="o">==</span> <span class="mi">0</span> <span class="kr">end</span><span class="p">,</span>
<span class="n">enumerate</span><span class="p">(</span><span class="n">duplicate</span><span class="p">(</span><span class="s1">'x'</span><span class="p">)))))</span>
<span class="mi">3</span> <span class="n">x</span>
<span class="mi">6</span> <span class="n">x</span>
<span class="mi">9</span> <span class="n">x</span>
<span class="mi">12</span> <span class="n">x</span>
<span class="mi">15</span> <span class="n">x</span>
</pre></div>
</div>
<div class="admonition note">
<p class="admonition-title">Note</p>
<p>Multireturn iterators are supported but can cause performance
regressions.</p>
</div>
<div class="admonition seealso">
<p class="admonition-title">See also</p>
<p><a class="reference internal" href="slicing.html#fun.take_while" title="fun.take_while"><code class="xref py py-func docutils literal notranslate"><span class="pre">take_while()</span></code></a> and <a class="reference internal" href="slicing.html#fun.drop_while" title="fun.drop_while"><code class="xref py py-func docutils literal notranslate"><span class="pre">drop_while()</span></code></a>.</p>
</div>
</dd></dl>
<dl class="py function">
<dt class="sig sig-object py" id="fun.remove_if">
<span class="sig-prename descclassname"><span class="pre">fun.</span></span><span class="sig-name descname"><span class="pre">remove_if</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">predicate</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">gen</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">param</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">state</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#fun.remove_if" title="Permalink to this definition">¶</a></dt>
<dt class="sig sig-object py">
<span class="sig-name descname"><span class="pre">iterator:remove_if(predicate)</span></span></dt>
<dd><p>An alias for <a class="reference internal" href="#fun.filter" title="fun.filter"><code class="xref py py-func docutils literal notranslate"><span class="pre">filter()</span></code></a>.</p>
</dd></dl>
<dl class="py function">
<dt class="sig sig-object py" id="fun.grep">
<span class="sig-prename descclassname"><span class="pre">fun.</span></span><span class="sig-name descname"><span class="pre">grep</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">regexp_or_predicate</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">gen</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">param</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">state</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#fun.grep" title="Permalink to this definition">¶</a></dt>
<dt class="sig sig-object py">
<span class="sig-name descname"><span class="pre">iterator:grep(regexp_or_predicate)</span></span></dt>
<dd><p>If <strong>regexp_or_predicate</strong> is string then the parameter is used as a regular
expression to build filtering predicate. Otherwise the function is just an
alias for <a class="reference internal" href="#fun.filter" title="fun.filter"><code class="xref py py-func docutils literal notranslate"><span class="pre">filter()</span></code></a>.</p>
<p>Equivalent to:</p>
<div class="highlight-lua notranslate"><div class="highlight"><pre><span></span><span class="kd">local</span> <span class="n">fun</span> <span class="o">=</span> <span class="n">regexp_or_predicate</span>
<span class="kr">if</span> <span class="nb">type</span><span class="p">(</span><span class="n">regexp_or_predicate</span><span class="p">)</span> <span class="o">==</span> <span class="s2">"string"</span> <span class="kr">then</span>
<span class="n">fun</span> <span class="o">=</span> <span class="kr">function</span><span class="p">(</span><span class="n">x</span><span class="p">)</span> <span class="kr">return</span> <span class="nb">string.find</span><span class="p">(</span><span class="n">x</span><span class="p">,</span> <span class="n">regexp_or_predicate</span><span class="p">)</span> <span class="o">~=</span> <span class="kc">nil</span> <span class="kr">end</span>
<span class="kr">end</span>
<span class="kr">return</span> <span class="n">filter</span><span class="p">(</span><span class="n">fun</span><span class="p">,</span> <span class="n">gen</span><span class="p">,</span> <span class="n">param</span><span class="p">,</span> <span class="n">state</span><span class="p">)</span>
</pre></div>
</div>
<p>Examples:</p>
<div class="highlight-lua notranslate"><div class="highlight"><pre><span></span><span class="n">lines_to_grep</span> <span class="o">=</span> <span class="p">{</span>
<span class="s">[[Emily]]</span><span class="p">,</span>
<span class="s">[[Chloe]]</span><span class="p">,</span>
<span class="s">[[Megan]]</span><span class="p">,</span>
<span class="s">[[Jessica]]</span><span class="p">,</span>
<span class="s">[[Emma]]</span><span class="p">,</span>
<span class="s">[[Sarah]]</span><span class="p">,</span>
<span class="s">[[Elizabeth]]</span><span class="p">,</span>
<span class="s">[[Sophie]]</span><span class="p">,</span>
<span class="s">[[Olivia]]</span><span class="p">,</span>
<span class="s">[[Lauren]]</span>
<span class="p">}</span>
<span class="n">each</span><span class="p">(</span><span class="nb">print</span><span class="p">,</span> <span class="n">grep</span><span class="p">(</span><span class="s2">"^Em"</span><span class="p">,</span> <span class="n">lines_to_grep</span><span class="p">))</span>
<span class="cm">--[[test</span>
<span class="cm">Emily</span>
<span class="cm">Emma</span>
<span class="cm">--test]]</span>
<span class="n">each</span><span class="p">(</span><span class="nb">print</span><span class="p">,</span> <span class="n">grep</span><span class="p">(</span><span class="s2">"^P"</span><span class="p">,</span> <span class="n">lines_to_grep</span><span class="p">))</span>
<span class="cm">--[[test</span>
<span class="cm">--test]]</span>
<span class="o">></span> <span class="n">each</span><span class="p">(</span><span class="nb">print</span><span class="p">,</span> <span class="n">grep</span><span class="p">(</span><span class="kr">function</span><span class="p">(</span><span class="n">x</span><span class="p">)</span> <span class="kr">return</span> <span class="n">x</span> <span class="o">%</span> <span class="mi">3</span> <span class="o">==</span> <span class="mi">0</span> <span class="kr">end</span><span class="p">,</span> <span class="n">range</span><span class="p">(</span><span class="mi">10</span><span class="p">)))</span>
<span class="mi">3</span>
<span class="mi">6</span>
<span class="mi">9</span>
</pre></div>
</div>
</dd></dl>
<dl class="py function">
<dt class="sig sig-object py" id="fun.partition">
<span class="sig-prename descclassname"><span class="pre">fun.</span></span><span class="sig-name descname"><span class="pre">partition</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">predicate</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">gen</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">param</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">state</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#fun.partition" title="Permalink to this definition">¶</a></dt>
<dt class="sig sig-object py">
<span class="sig-name descname"><span class="pre">iterator:partition(predicate)</span></span></dt>
<dd><dl class="field-list simple">
<dt class="field-odd">Parameters</dt>
<dd class="field-odd"><p><strong>x</strong> – a value to find</p>
</dd>
<dt class="field-even">Returns</dt>
<dd class="field-even"><p>{gen1, param1, state1}, {gen2, param2, state2}</p>
</dd>
</dl>
<p>The function returns two iterators where elements do and do not satisfy the
prediucate. Equivalent to:</p>
<div class="highlight-lua notranslate"><div class="highlight"><pre><span></span><span class="kr">return</span> <span class="n">filter</span><span class="p">(</span><span class="n">predicate</span><span class="p">,</span> <span class="n">gen</span><span class="s1">', param'</span><span class="p">,</span> <span class="n">state</span><span class="s1">'),</span>
<span class="s1">filter(function(...) return not predicate(...) end, gen, param, state);</span>
</pre></div>
</div>
<p>The function make a clone of the source iterator. Iterators especially
returned in tables to work with <a class="reference internal" href="compositions.html#fun.zip" title="fun.zip"><code class="xref py py-func docutils literal notranslate"><span class="pre">zip()</span></code></a> and other functions.</p>
<p>Examples:</p>
<div class="highlight-lua notranslate"><div class="highlight"><pre><span></span><span class="o">></span> <span class="n">each</span><span class="p">(</span><span class="nb">print</span><span class="p">,</span> <span class="n">zip</span><span class="p">(</span><span class="n">partition</span><span class="p">(</span><span class="kr">function</span><span class="p">(</span><span class="n">i</span><span class="p">,</span> <span class="n">x</span><span class="p">)</span> <span class="kr">return</span> <span class="n">i</span> <span class="o">%</span> <span class="mi">3</span> <span class="o">==</span> <span class="mi">0</span> <span class="kr">end</span><span class="p">,</span> <span class="n">range</span><span class="p">(</span><span class="mi">10</span><span class="p">))))</span>
<span class="mi">3</span> <span class="mi">1</span>
<span class="mi">6</span> <span class="mi">2</span>
<span class="mi">9</span> <span class="mi">4</span>
</pre></div>
</div>
<div class="admonition note">
<p class="admonition-title">Note</p>
<p><code class="docutils literal notranslate"><span class="pre">gen,</span> <span class="pre">param,</span> <span class="pre">state</span></code> must be pure functional to work properly
with the function.</p>
</div>
<div class="admonition seealso">
<p class="admonition-title">See also</p>
<p><a class="reference internal" href="slicing.html#fun.span" title="fun.span"><code class="xref py py-func docutils literal notranslate"><span class="pre">span()</span></code></a></p>
</div>
</dd></dl>
</section>
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