php-doc-en/reference/array/functions/array-diff.xml

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<refentry xml:id="function.array-diff" xmlns="http://docbook.org/ns/docbook">
 <refnamediv>
  <refname>array_diff</refname>
  <refpurpose>Computes the difference of arrays</refpurpose>
 </refnamediv>

 <refsect1 role="description">
  &reftitle.description;
  <methodsynopsis>
   <type>array</type><methodname>array_diff</methodname>
   <methodparam><type>array</type><parameter>array</parameter></methodparam>
   <methodparam rep="repeat"><type>array</type><parameter>arrays</parameter></methodparam>
  </methodsynopsis>
  <para>
   Compares <parameter>array</parameter> against one or more other arrays and
   returns the values in <parameter>array</parameter> that are not present in
   any of the other arrays.
  </para>
 </refsect1>

 <refsect1 role="parameters">
  &reftitle.parameters;
  <para>
   <variablelist>
    <varlistentry>
     <term><parameter>array</parameter></term>
     <listitem>
      <para>
       The array to compare from
      </para>
     </listitem>
    </varlistentry>
    <varlistentry>
     <term><parameter>arrays</parameter></term>
     <listitem>
      <para>
       Arrays to compare against
      </para>
     </listitem>
    </varlistentry>
   </variablelist>
  </para>
 </refsect1>

 <refsect1 role="returnvalues">
  &reftitle.returnvalues;
  <para>
   Returns an <type>array</type> containing all the entries from
   <parameter>array</parameter> that are not present in any of the other arrays.
   Keys in the <parameter>array</parameter> array are preserved.
  </para>
 </refsect1>

 <refsect1 role="examples">
  &reftitle.examples;
  <para>
   <example>
    <title><function>array_diff</function> example</title>
    <programlisting role="php">
<![CDATA[
<?php
$array1 = array("a" => "green", "red", "blue", "red");
$array2 = array("b" => "green", "yellow", "red");
$result = array_diff($array1, $array2);

print_r($result);
?>
]]>
    </programlisting>
    <para>
     Multiple occurrences in <varname>$array1</varname> are all
     treated the same way. This will output :
    </para>
    <screen>
<![CDATA[
Array
(
    [1] => blue
)
]]>
    </screen>
   </example>
  </para>

  <para>
   <example>
    <title><function>array_diff</function> example with non-matching types</title>
    <para>
     Two elements are considered equal if and only if
     <literal>(string) $elem1 === (string) $elem2</literal>. That is,
     when the <link linkend="language.types.string.casting">string representation</link> is the same.
    </para>
    <programlisting role="php">
     <![CDATA[
<?php
// This will generate a Notice that an array cannot be cast to a string.
$source = [1, 2, 3, 4];
$filter = [3, 4, [5], 6];
$result = array_diff($source, $filter);

// Whereas this is fine, since the objects can cast to a string.
class S {
  private $v;

  public function __construct(string $v) {
    $this->v = $v;
  }

  public function __toString() {
    return $this->v;
  }
}

$source = [new S('a'), new S('b'), new S('c')];
$filter = [new S('b'), new S('c'), new S('d')];

$result = array_diff($source, $filter);

// $result now contains one instance of S('a');
?>
]]>
    </programlisting>
    <para>
     To use an alternate comparison function, see <function>array_udiff</function>.
    </para>
   </example>
  </para>
 </refsect1>

 <refsect1 role="notes">
  &reftitle.notes;
  <note>
   <para>
    This function only checks one dimension of a n-dimensional
    array. Of course you can check deeper dimensions by using
    <literal>array_diff($array1[0], $array2[0]);</literal>.
   </para>
  </note>
 </refsect1>

 <refsect1 role="seealso">
  &reftitle.seealso;
  <para>
   <simplelist>
    <member><function>array_diff_assoc</function></member>
    <member><function>array_udiff</function></member>
    <member><function>array_intersect</function></member>
    <member><function>array_intersect_assoc</function></member>
   </simplelist>
  </para>
 </refsect1>

</refentry>

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