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<refentry xml:id="function.array-multisort" xmlns="http://docbook.org/ns/docbook">
<refnamediv>
<refname>array_multisort</refname>
<refpurpose>Sort multiple or multi-dimensional arrays</refpurpose>
</refnamediv>
<refsect1 role="description">
&reftitle.description;
<methodsynopsis>
<type>bool</type><methodname>array_multisort</methodname>
<methodparam><type>array</type><parameter role="reference">arr</parameter></methodparam>
<methodparam choice="opt"><type>mixed</type><parameter>arg</parameter><initializer>SORT_ASC</initializer></methodparam>
<methodparam choice="opt"><type>mixed</type><parameter>arg</parameter><initializer>SORT_REGULAR</initializer></methodparam>
<methodparam choice="opt"><type>mixed</type><parameter>...</parameter></methodparam>
</methodsynopsis>
<para>
<function>array_multisort</function> can be used to sort several
arrays at once, or a multi-dimensional array by one or more
dimensions.
</para>
<para>
Associative (<type>string</type>) keys will be maintained, but numeric
keys will be re-indexed.
</para>
</refsect1>
<refsect1 role="parameters">
&reftitle.parameters;
<para>
<variablelist>
<varlistentry>
<term><parameter>arr</parameter></term>
<listitem>
<para>
An <type>array</type> being sorted.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><parameter>arg</parameter></term>
<listitem>
<para>
Optionally another <type>array</type>, or sort options for the
previous <type>array</type> argument:
<constant>SORT_ASC</constant>,
<constant>SORT_DESC</constant>,
<constant>SORT_REGULAR</constant>,
<constant>SORT_NUMERIC</constant>,
<constant>SORT_STRING</constant>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><parameter>...</parameter></term>
<listitem>
<para>
Additional <parameter>arg</parameter>'s.
</para>
</listitem>
</varlistentry>
</variablelist>
</para>
</refsect1>
<refsect1 role="returnvalues">
&reftitle.returnvalues;
<para>
&return.success;
</para>
</refsect1>
<refsect1 role="examples">
&reftitle.examples;
<para>
<example>
<title>Sorting multiple arrays</title>
<programlisting role="php">
<![CDATA[
<?php
$ar1 = array(10, 100, 100, 0);
$ar2 = array(1, 3, 2, 4);
array_multisort($ar1, $ar2);
var_dump($ar1);
var_dump($ar2);
?>
]]>
</programlisting>
<para>
In this example, after sorting, the first array will contain 0,
10, 100, 100. The second array will contain 4, 1, 2, 3. The
entries in the second array corresponding to the identical
entries in the first array (100 and 100) were sorted as well.
</para>
<screen>
<![CDATA[
array(4) {
[0]=> int(0)
[1]=> int(10)
[2]=> int(100)
[3]=> int(100)
}
array(4) {
[0]=> int(4)
[1]=> int(1)
[2]=> int(2)
[3]=> int(3)
}
]]>
</screen>
</example>
</para>
<para>
<example>
<title>Sorting multi-dimensional array</title>
<programlisting role="php">
<![CDATA[
<?php
$ar = array(
array("10", 11, 100, 100, "a"),
array( 1, 2, "2", 3, 1)
);
array_multisort($ar[0], SORT_ASC, SORT_STRING,
$ar[1], SORT_NUMERIC, SORT_DESC);
var_dump($ar);
?>
]]>
</programlisting>
<para>
In this example, after sorting, the first array will transform to
"10", 100, 100, 11, "a" (it was sorted as strings in ascending
order). The second will contain 1, 3, "2", 2, 1 (sorted as numbers,
in descending order).
</para>
<screen>
<![CDATA[
array(2) {
[0]=> array(5) {
[0]=> string(2) "10"
[1]=> int(100)
[2]=> int(100)
[3]=> int(11)
[4]=> string(1) "a"
}
[1]=> array(5) {
[0]=> int(1)
[1]=> int(3)
[2]=> string(1) "2"
[3]=> int(2)
[4]=> int(1)
}
}
]]>
</screen>
</example>
</para>
<para>
<example>
<title>Sorting database results</title>
<para>
For this example, each element in the <varname>data</varname>
array represents one row in a table. This type of dataset is typical
of database records.
</para>
<para>
Example data:
</para>
<screen>
<![CDATA[
volume | edition
-------+--------
67 | 2
86 | 1
85 | 6
98 | 2
86 | 6
67 | 7
]]>
</screen>
<para>
The data as an array, called <varname>data</varname>. This would usually,
for example, be obtained by looping with <function>mysql_fetch_assoc</function>.
</para>
<programlisting role="php">
<![CDATA[
<?php
$data[] = array('volume' => 67, 'edition' => 2);
$data[] = array('volume' => 86, 'edition' => 1);
$data[] = array('volume' => 85, 'edition' => 6);
$data[] = array('volume' => 98, 'edition' => 2);
$data[] = array('volume' => 86, 'edition' => 6);
$data[] = array('volume' => 67, 'edition' => 7);
?>
]]>
</programlisting>
<para>
In this example, we will order by <varname>volume</varname> descending,
<varname>edition</varname> ascending.
</para>
<para>
We have an array of rows, but <function>array_multisort</function>
requires an array of columns, so we use the below code to obtain the
columns, then perform the sorting.
</para>
<programlisting role="php">
<![CDATA[
<?php
// Obtain a list of columns
foreach ($data as $key => $row) {
$volume[$key] = $row['volume'];
$edition[$key] = $row['edition'];
}
// Sort the data with volume descending, edition ascending
// Add $data as the last parameter, to sort by the common key
array_multisort($volume, SORT_DESC, $edition, SORT_ASC, $data);
?>
]]>
</programlisting>
<para>
The dataset is now sorted, and will look like this:
</para>
<screen>
<![CDATA[
volume | edition
-------+--------
98 | 2
86 | 1
86 | 6
85 | 6
67 | 2
67 | 7
]]>
</screen>
</example>
</para>
<para>
<example>
<title>Case insensitive sorting</title>
<para>
Both <constant>SORT_STRING</constant> and
<constant>SORT_REGULAR</constant> are case sensitive, strings
starting with a capital letter will come before strings starting
with a lowercase letter.
</para>
<para>
To perform a case insensitive search, force the sorting order to be
determined by a lowercase copy of the original array.
</para>
<programlisting role="php">
<![CDATA[
<?php
$array = array('Alpha', 'atomic', 'Beta', 'bank');
$array_lowercase = array_map('strtolower', $array);
array_multisort($array_lowercase, SORT_ASC, SORT_STRING, $array);
print_r($array);
?>
]]>
</programlisting>
&example.outputs;
<screen>
<![CDATA[
Array
(
[0] => Alpha
[1] => atomic
[2] => bank
[3] => Beta
)
]]>
</screen>
</example>
</para>
</refsect1>
<refsect1 role="seealso">
&reftitle.seealso;
<para>
<simplelist>
<member><function>usort</function></member>
<member>&seealso.array.sorting;</member>
</simplelist>
</para>
</refsect1>
</refentry>
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