php-doc-en/reference/array/sorting.xml

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<chapter xml:id="array.sorting" xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink">
 <title>Sorting Arrays</title>
 <para>
  PHP has several functions that deal with sorting arrays, and this
  document exists to help sort it all out.
 </para>
 <para>
  The main differences are:
 </para>
 <para>
  <simplelist>
   <member>
    Some sort based on the <type>array</type> keys, whereas others by
    the values: <literal>$array['key'] = 'value';</literal>
   </member>
   <member>
    Whether or not the correlation between the keys and values are
    maintained after the sort, which may mean the keys are reset
    numerically (0,1,2 ...)
   </member>
   <member>
    The order of the sort: alphabetical, low to high (ascending),
    high to low (descending), numerical, natural, random, or user defined
   </member>
   <member>
    Note: All of these sort functions act directly on the array
    variable itself, as opposed to returning a new sorted array
   </member>
   <member>
    If any of these sort functions evaluates two members as equal then the
    order is undefined (the sorting is not stable).
   </member>
  </simplelist>
 </para>
 <para>
  <table>
   <title>Sorting function attributes</title>
   <tgroup cols="5">
    <thead>
     <row>
      <entry>Function name</entry>
      <entry>Sorts by</entry>
      <entry>Maintains key association</entry>
      <entry>Order of sort</entry>
      <entry>Related functions</entry>
     </row>
    </thead>
    <tbody>
     <row>
      <entry><function>array_multisort</function></entry>
      <entry>value</entry>
      <entry>associative yes, numeric no</entry>
      <entry>first array or sort options</entry>
      <entry><function>array_walk</function></entry>
     </row>
     <row>
      <entry><function>asort</function></entry>
      <entry>value</entry>
      <entry>yes</entry>
      <entry>low to high</entry>
      <entry><function>arsort</function></entry>
     </row>
     <row>
      <entry><function>arsort</function></entry>
      <entry>value</entry>
      <entry>yes</entry>
      <entry>high to low</entry>
      <entry><function>asort</function></entry>
     </row>
     <row>
      <entry><function>krsort</function></entry>
      <entry>key</entry>
      <entry>yes</entry>
      <entry>high to low</entry>
      <entry><function>ksort</function></entry>
     </row>
     <row>
      <entry><function>ksort</function></entry>
      <entry>key</entry>
      <entry>yes</entry>
      <entry>low to high</entry>
      <entry><function>asort</function></entry>
     </row>
     <row>
      <entry><function>natcasesort</function></entry>
      <entry>value</entry>
      <entry>yes</entry>
      <entry>natural, case insensitive</entry>
      <entry><function>natsort</function></entry>
     </row>
     <row>
      <entry><function>natsort</function></entry>
      <entry>value</entry>
      <entry>yes</entry>
      <entry>natural</entry>
      <entry><function>natcasesort</function></entry>
     </row>
     <row>
      <entry><function>rsort</function></entry>
      <entry>value</entry>
      <entry>no</entry>
      <entry>high to low</entry>
      <entry><function>sort</function></entry>
     </row>
     <row>
      <entry><function>shuffle</function></entry>
      <entry>value</entry>
      <entry>no</entry>
      <entry>random</entry>
      <entry><function>array_rand</function></entry>
     </row>
     <row>
      <entry><function>sort</function></entry>
      <entry>value</entry>
      <entry>no</entry>
      <entry>low to high</entry>
      <entry><function>rsort</function></entry>
     </row>
     <row>
      <entry><function>uasort</function></entry>
      <entry>value</entry>
      <entry>yes</entry>
      <entry>user defined</entry>
      <entry><function>uksort</function></entry>
     </row>
     <row>
      <entry><function>uksort</function></entry>
      <entry>key</entry>
      <entry>yes</entry>
      <entry>user defined</entry>
      <entry><function>uasort</function></entry>
     </row>
     <row>
      <entry><function>usort</function></entry>
      <entry>value</entry>
      <entry>no</entry>
      <entry>user defined</entry>
      <entry><function>uasort</function></entry>
     </row>
    </tbody>
   </tgroup>
  </table>
 </para>
</chapter>

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