Array Functions

PHP uasort() Function

Topic: PHP Array ReferencePrev|Next


The uasort() function sorts an array by values using a user-defined comparison function.

The keys are preserved, i.e. the key-to-value mapping will remain unchanged by the sort operation.

The following table summarizes the technical details of this function.

Return Value: Returns TRUE on success or FALSE on failure.
Version: PHP 4+


The basic syntax of the uasort() function is given with:

uasort(array, compare_function);

The following example shows the uasort() function in action.

// Define comparison function
function compare($a, $b){
    if($a == $b){
        return 0;
    return ($a < $b) ? -1 : 1;

// Sample array
$numbers = array("a"=>2, "b"=>-1, "c"=>7, "d"=>-9, "e"=>5, "f"=>-4);

// Sort numbers array using compare function
uasort($numbers, "compare");

The uasort() function is mainly used for sorting associative arrays by value. To sort an associative array by keys using a user-defined comparison function use the uksort() function.

Note: The comparison function must return an integer equal to zero if both values are equal, an integer less than zero if the first value is less than the second value, and an integer greater than zero if the first value is greater than the second value.


The uasort() function accepts the following parameters.

Parameter Description
array Required. Specifies the array to be sorted.
compare_function Optional. Specifies the compare function to use for sorting.
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