array-find-key.xml

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<refentry xml:id="function.array-find-key" xmlns="http://docbook.org/ns/docbook">
 <refnamediv>
  <refname>array_find_key</refname>
  <refpurpose>Returns the key of the first element satisfying a callback function</refpurpose>
 </refnamediv>

 <refsect1 role="description">
  &reftitle.description;
  <methodsynopsis>
   <type>mixed</type><methodname>array_find_key</methodname>
   <methodparam><type>array</type><parameter>array</parameter></methodparam>
   <methodparam><type>callable</type><parameter>callback</parameter></methodparam>
  </methodsynopsis>
  <simpara>
   <function>array_find_key</function> returns the key of the first element of an
   &array; for which the given <parameter>callback</parameter> returns &true;.
   If no matching element is found the function returns &null;.
  </simpara>
 </refsect1>

 <refsect1 role="parameters">
  &reftitle.parameters;
  <variablelist>
   <varlistentry>
    <term><parameter>array</parameter></term>
    <listitem>
     <simpara>
      The &array; that should be searched.
     </simpara>
    </listitem>
   </varlistentry>
   <varlistentry>
    <term><parameter>callback</parameter></term>
    <listitem>
     <para>
      The callback function to call to check each element, which must be
      <methodsynopsis>
       <type>bool</type><methodname><replaceable>callback</replaceable></methodname>
       <methodparam><type>mixed</type><parameter>value</parameter></methodparam>
       <methodparam><type>mixed</type><parameter>key</parameter></methodparam>
      </methodsynopsis>
      If this function returns &true;, the key is returned from
      <function>array_find_key</function> and the callback will not be called
      for further elements.
     </para>
    </listitem>
   </varlistentry>
  </variablelist>
 </refsect1>

 <refsect1 role="returnvalues">
  &reftitle.returnvalues;
  <simpara>
   The function returns the key of the first element for which the
   <parameter>callback</parameter> returns &true;. If no matching element is
   found the function returns &null;.
  </simpara>
 </refsect1>

 <refsect1 role="examples">
  &reftitle.examples;
  <example>
   <title><function>array_find_key</function> example</title>
   <programlisting role="php">
<![CDATA[
<?php
$array = [
    'a' => 'dog',
    'b' => 'cat',
    'c' => 'cow',
    'd' => 'duck',
    'e' => 'goose',
    'f' => 'elephant'
];

// Find the first animal with a name longer than 4 characters.
var_dump(array_find_key($array, function (string $value) {
    return strlen($value) > 4;
}));

// Find the first animal whose name begins with f.
var_dump(array_find_key($array, function (string $value) {
    return str_starts_with($value, 'f');
}));

// Find the first animal where the array key is the first symbol of the animal.
var_dump(array_find_key($array, function (string $value, $key) {
   return $value[0] === $key;
}));

// Find the first animal where the array key matching a RegEx.
var_dump(array_find_key($array, function ($value, $key) {
   return preg_match('/^([a-f])$/', $key);
}));
?>
]]>
   </programlisting>
   &example.outputs;
   <screen>
<![CDATA[
string(1) "e"
NULL
string(1) "c"
string(1) "a"
]]>
   </screen>
  </example>
 </refsect1>

 <refsect1 role="seealso">
  &reftitle.seealso;
  <simplelist>
   <member><function>array_find</function></member>
   <member><function>array_all</function></member>
   <member><function>array_any</function></member>
   <member><function>array_filter</function></member>
   <member><function>array_reduce</function></member>
  </simplelist>
 </refsect1>
</refentry>
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