How to sort a multidimensional array by a specific value using PHP

Sorting a multidimentional array by a specific value using PHP is quite simple once you get your head around the functions required to do so.  The two functions involved are ‘usort’ & ‘strcasecmp’, these will be discussed at a later stage in the tutorial.

Sort a multidimensional array by a specific value

The first thing we need is an array like the one shown below. As you can see it contains a number of sub-arrays. Let’s say, for the purpose of this tutorial, that our aim is to sort the array by the ‘name’ field.

$array = array(
		1 => array(
				"name" => "dave",
				"id" => 23,
				"company" => "Subway"
			),
		2 => array(
				"name" => "Allan",
				"id" => 2,
				"company" => "Mothercare"
			),
		3 => array(
				"name" => "Kate",
				"id" => 15,
				"company" => "Stagecoach"
			),
		4=> array(
				"name" => "Craig",
				"id" => 1,
				"company" => "Stagecoach"
			)
	     );

The below code will sort the array using the name field, and will do so in a case insensitive manner.

function sortByName($a, $b) {
	return strcasecmp($a['name'], $b['name']);
}
usort($array, "sortByName");

 Sorting a multidimensional array by a specific value is as simple as that, so if you were looking for a quick cut-and-paste job you are done already. However, if you are looking at the function and don’t understand how it works then read on!

The result:

array
  0 => 
    array
      'name' => string 'Allan' (length=5)
      'id' => int 2
      'company' => string 'Mothercare' (length=10)
  1 => 
    array
      'name' => string 'Craig' (length=5)
      'id' => int 1
      'company' => string 'Stagecoach' (length=10)
  2 => 
    array
      'name' => string 'dave' (length=4)
      'id' => int 23
      'company' => string 'Subway' (length=6)
  3 => 
    array
      'name' => string 'Kate' (length=4)
      'id' => int 15
      'company' => string 'Stagecoach' (length=10)

Let’s start with the ‘usort()’ function.

How the usort function works

As you can see above the ‘usort’ function accepts two parameters. The first is the array which is to be sorted, and the second is the (user defined) callback function which will be used to sort the array. The quote below is taken from the php.net documentation and explains exactly what this callback function should do.

The comparison function must return an integer less than, equal to, or greater than zero if the first argument is considered to be respectively less than, equal to, or greater than the second.

So, what is happening is that the callback function is being passed two entities from the array at a time. Let’s call them $a, and $b as in the example above. When given these two entities the function should do the following:

• If $a is less than $b, return -1 (or less).
• If $a is equal to $b, return 0.
• If $a is greater than $b, return 1(or more).

How the strcasecmp function works

The ‘strcasecmp’ function is used for case insensitive string comparison, below is an overview of how it works.

Returns < 0 if str1 is less than str2; > 0 if str1 is greater than str2, and 0 if they are equal.

So, the function returns the exact values required for use in the ‘usort’ function. Very handy!

Recap: When given two values, again let’s call them $a and $b the function does the following:

• If $a is less than $b, return -1 (or less).
• If $a is equal to $b, return 0.
• If $a is greater than $b, return 1(or more).

Using these return values the usort function is able to determine the greater value between $a and $b and thus place them in the correct order.

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