PHP 4, PHP 5, PHP 7, PHP 8
usort - Sort an array by values using a user-defined comparison function
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usort( arrayarray, callable$callback ): bool

Sorts array in place by values using a user-supplied comparison function to determine the order.


If two members compare as equal, they retain their original order. Prior to PHP 8.0.0, their relative order in the sorted array was undefined.


This function assigns new keys to the elements in array. It will remove any existing keys that may have been assigned, rather than just reordering the keys.



The input array.


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.

callback(mixed$a,mixed$b ): int

Return Values

Always returns true.


Version Description
8.0.0 If callback expects a parameter to be passed by reference, this function will now emit an E_WARNING.

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Example of usort

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