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PHP support for arrays is fantastic, particularly for those of us with a history using ASP. Sorting a single-column array is straightforward (there is a sort() function). But what about sorting a multi-column array? Well, there is a function (array_multisort()) that does it, but understanding how to use it is a challenge. This article hopefully provides a simpler explanation.

If you are using a multi-column array to store data from a database, it is much simpler and faster to get the data directly from the database in the order required (use the ORDER BY clause in your SELECT statement).  This function is best used for multi-column arrays that are generated locally, or only in part from a database.

How to

To sort a multi-column array:

1. determine which columns you want to sort by
2. for each column you want to sort by, copy its contents into a separate, single-column array
3. build your array_multisort() command:
• add the new single-column array as a parameter
• optionally follow the array with parameters for sort order and type
• repeat above two steps for each column to be sorted on
• complete command with name of multi-column array to be sorted

sort type and order

Sort type can be:

• SORT_REGULAR – compare/sort normally (default)
• SORT_NUMERIC – compare/sort as numbers
• SORT_STRING – compare/sort as strings

Sort regular uses standard ASCII order (“ABa” is 3 characters in regular order). The other two options operate more logically (eg “aAB” is the same characters now in string order).

Sort order can be:

• SORT_ASC – ascending order (default)
• SORT_DESC – descending order

For example…

For example. here’s a 3-column array we want to sort:

<?php
  $data[0]['name']= 'Google';
  $data[0]['url'] = 'http://www.google.com';
  $data[0]['rank'] = 45;

  $data[1]['name']= 'Yahoo';
  $data[1]['url'] = 'http://www.yahoo.com';
  $data[1]['rank'] = 17;

  $data[2]['name']= 'MSN';
  $data[2]['url'] = 'http://www.msn.com';
  $data[2]['rank'] = 6;
?>

Assume we want to sort this array by rank (ascending order). The first step is to store the rank column as a separate, single-column array. This is easy to do using the foreach command:

<?php
  foreach ($data as $val)
  {
    $sortArrayRank[] = $val['rank'];
  }
?>

To sort by this column, use array_multisort and pass our newly created rank array as the first parameter:

<?php
  array_multisort($sortArrayRank, $data);
?>

To change the sort to descending order, add the required order parameter after the 1-column array:

<?php
  array_multisort($sortArrayRank, SORT_DESC, $data);
?>

To sort by more than one column (eg to sort by rank, then name), simply repeat the above steps for the subsequent column(s) and add the paramaters to the list.

<?php
  foreach ($data as $val)
  {
    $sortArrayName[] = $val['name'];
  }
  array_multisort($sortArrayRank, SORT_DESC, $sortArrayName, $data);
?>

more information

The official explanation of array_multisort can be found in the PHP manual.