The usort Function

The usort function sorts an array by element values, using a callback to determine the order of elements in the sorted array. The function modifies the array itself.

The comparison function must return an integer, which depending on the comparison result: less than, equal to, or greater than zero.

Syntax

phpusort(array &$array, callable $callback): bool

Example

Let's sort an array in ascending order of elements:

php<?php
  $arr = [1, 3, 2, 5, 4];
  
  function func($a, $b)
  {
    if ($a === $b) {
      return 0;
    } else if ($a < $b) {
      return -1;
    } else {
      return 1;
    }
  }
  
  usort($arr, 'func');
  var_dump($arr);
?>

Code execution result:

php[1, 2, 3, 4, 5]

Example

Now let's sort an array in descending order of elements:

php<?php
  $arr = [1, 3, 2, 5, 4];
  
  function func($a, $b)
  {
    if ($a === $b) {
      return 0;
    } else if ($a > $b) {
      return -1;
    } else {
      return 1;
    }
  }
  
  usort($arr, 'func');
  var_dump($arr);
?>

Code execution result:

php[1, 2, 3, 4, 5]

Example

Now let's sort an array by ascending number of characters in the array elements:

php<?php
  $arr = [
    '123',
    '1',
    '12345',
    '12',
    '1234',
  ];
  
  function func($a, $b)
  {
    if (strlen($a) === strlen($b)) {
      return 0;
    } else if (strlen($a) < strlen($b)) {
      return -1;
    } else {
      return 1;
    }
  }
  
  usort($arr, 'func');
  var_dump($arr);
?>

Code execution result:

php[
  '1',
  '12',
  '123',
  '1234',
  '12345',
]

See Also