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<title>Iteratively reduce the array to a single value using a callback function</title>
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<h1 class="refname">array_reduce</h1>
<p class="verinfo">(PHP 4 >= 4.0.5, PHP 5, PHP 7)</p><p class="refpurpose"><span class="refname">array_reduce</span> — <span class="dc-title">Iteratively reduce the array to a single value using a callback function</span></p>
</div>
<div class="refsect1 description" id="refsect1-function.array-reduce-description">
<h3 class="title">Description</h3>
<div class="methodsynopsis dc-description">
<span class="type"><a href="language.pseudo-types.html#language.types.mixed" class="type mixed">mixed</a></span> <span class="methodname"><strong>array_reduce</strong></span>
( <span class="methodparam"><span class="type">array</span> <code class="parameter">$array</code></span>
, <span class="methodparam"><span class="type"><a href="language.types.callable.html" class="type callable">callable</a></span> <code class="parameter">$callback</code></span>
[, <span class="methodparam"><span class="type"><a href="language.pseudo-types.html#language.types.mixed" class="type mixed">mixed</a></span> <code class="parameter">$initial</code><span class="initializer"> = <strong><code>NULL</code></strong></span></span>
] )</div>
<p class="para rdfs-comment">
<span class="function"><strong>array_reduce()</strong></span> applies iteratively the
<code class="parameter">callback</code> function to the elements of the
<code class="parameter">array</code>, so as to reduce the array to
a single value.
</p>
</div>
<div class="refsect1 parameters" id="refsect1-function.array-reduce-parameters">
<h3 class="title">Parameters</h3>
<p class="para">
<dl>
<dt>
<code class="parameter">array</code></dt>
<dd>
<p class="para">
The input array.
</p>
</dd>
<dt>
<code class="parameter">callback</code></dt>
<dd>
<div class="methodsynopsis dc-description">
<span class="type"><a href="language.pseudo-types.html#language.types.mixed" class="type mixed">mixed</a></span> <span class="methodname"><span class="replaceable">callback</span></span>
( <span class="methodparam"><span class="type"><a href="language.pseudo-types.html#language.types.mixed" class="type mixed">mixed</a></span> <code class="parameter">$carry</code></span>
, <span class="methodparam"><span class="type"><a href="language.pseudo-types.html#language.types.mixed" class="type mixed">mixed</a></span> <code class="parameter">$item</code></span>
)</div>
<dl>
<dt>
<code class="parameter">carry</code></dt>
<dd>
<p class="para">
Holds the return value of the previous iteration; in the case of the
first iteration it instead holds the value of
<code class="parameter">initial</code>.
</p>
</dd>
<dt>
<code class="parameter">item</code></dt>
<dd>
<p class="para">
Holds the value of the current iteration.
</p>
</dd>
</dl>
</dd>
<dt>
<code class="parameter">initial</code></dt>
<dd>
<p class="para">
If the optional <code class="parameter">initial</code> is available, it will
be used at the beginning of the process, or as a final result in case
the array is empty.
</p>
</dd>
</dl>
</p>
</div>
<div class="refsect1 returnvalues" id="refsect1-function.array-reduce-returnvalues">
<h3 class="title">Return Values</h3>
<p class="para">
Returns the resulting value.
</p>
<p class="para">
If the array is empty and <code class="parameter">initial</code> is not passed,
<span class="function"><strong>array_reduce()</strong></span> returns <strong><code>NULL</code></strong>.
</p>
</div>
<div class="refsect1 changelog" id="refsect1-function.array-reduce-changelog">
<h3 class="title">Changelog</h3>
<p class="para">
<table class="doctable informaltable">
<thead>
<tr>
<th>Version</th>
<th>Description</th>
</tr>
</thead>
<tbody class="tbody">
<tr>
<td>5.3.0</td>
<td>
Changed <code class="parameter">initial</code> to allow <span class="type"><a href="language.pseudo-types.html#language.types.mixed" class="type mixed">mixed</a></span>, previously <span class="type"><a href="language.types.integer.html" class="type integer">integer</a></span>.
</td>
</tr>
</tbody>
</table>
</p>
</div>
<div class="refsect1 examples" id="refsect1-function.array-reduce-examples">
<h3 class="title">Examples</h3>
<p class="para">
<div class="example" id="example-6189">
<p><strong>Example #1 <span class="function"><strong>array_reduce()</strong></span> example</strong></p>
<div class="example-contents">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB"><?php<br /></span><span style="color: #007700">function </span><span style="color: #0000BB">sum</span><span style="color: #007700">(</span><span style="color: #0000BB">$carry</span><span style="color: #007700">, </span><span style="color: #0000BB">$item</span><span style="color: #007700">)<br />{<br /> </span><span style="color: #0000BB">$carry </span><span style="color: #007700">+= </span><span style="color: #0000BB">$item</span><span style="color: #007700">;<br /> return </span><span style="color: #0000BB">$carry</span><span style="color: #007700">;<br />}<br /><br />function </span><span style="color: #0000BB">product</span><span style="color: #007700">(</span><span style="color: #0000BB">$carry</span><span style="color: #007700">, </span><span style="color: #0000BB">$item</span><span style="color: #007700">)<br />{<br /> </span><span style="color: #0000BB">$carry </span><span style="color: #007700">*= </span><span style="color: #0000BB">$item</span><span style="color: #007700">;<br /> return </span><span style="color: #0000BB">$carry</span><span style="color: #007700">;<br />}<br /><br /></span><span style="color: #0000BB">$a </span><span style="color: #007700">= array(</span><span style="color: #0000BB">1</span><span style="color: #007700">, </span><span style="color: #0000BB">2</span><span style="color: #007700">, </span><span style="color: #0000BB">3</span><span style="color: #007700">, </span><span style="color: #0000BB">4</span><span style="color: #007700">, </span><span style="color: #0000BB">5</span><span style="color: #007700">);<br /></span><span style="color: #0000BB">$x </span><span style="color: #007700">= array();<br /><br /></span><span style="color: #0000BB">var_dump</span><span style="color: #007700">(</span><span style="color: #0000BB">array_reduce</span><span style="color: #007700">(</span><span style="color: #0000BB">$a</span><span style="color: #007700">, </span><span style="color: #DD0000">"sum"</span><span style="color: #007700">)); </span><span style="color: #FF8000">// int(15)<br /></span><span style="color: #0000BB">var_dump</span><span style="color: #007700">(</span><span style="color: #0000BB">array_reduce</span><span style="color: #007700">(</span><span style="color: #0000BB">$a</span><span style="color: #007700">, </span><span style="color: #DD0000">"product"</span><span style="color: #007700">, </span><span style="color: #0000BB">10</span><span style="color: #007700">)); </span><span style="color: #FF8000">// int(1200), because: 10*1*2*3*4*5<br /></span><span style="color: #0000BB">var_dump</span><span style="color: #007700">(</span><span style="color: #0000BB">array_reduce</span><span style="color: #007700">(</span><span style="color: #0000BB">$x</span><span style="color: #007700">, </span><span style="color: #DD0000">"sum"</span><span style="color: #007700">, </span><span style="color: #DD0000">"No data to reduce"</span><span style="color: #007700">)); </span><span style="color: #FF8000">// string(17) "No data to reduce"<br /></span><span style="color: #0000BB">?></span>
</span>
</code></div>
</div>
</div>
</p>
</div>
<div class="refsect1 seealso" id="refsect1-function.array-reduce-seealso">
<h3 class="title">See Also</h3>
<p class="para">
<ul class="simplelist">
<li class="member"><span class="function"><a href="function.array-filter.html" class="function" rel="rdfs-seeAlso">array_filter()</a> - Filters elements of an array using a callback function</span></li>
<li class="member"><span class="function"><a href="function.array-map.html" class="function" rel="rdfs-seeAlso">array_map()</a> - Applies the callback to the elements of the given arrays</span></li>
<li class="member"><span class="function"><a href="function.array-unique.html" class="function" rel="rdfs-seeAlso">array_unique()</a> - Removes duplicate values from an array</span></li>
<li class="member"><span class="function"><a href="function.array-count-values.html" class="function" rel="rdfs-seeAlso">array_count_values()</a> - Counts all the values of an array</span></li>
</ul>
</p>
</div>
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