PHP uasort() Function

The uasort() function is a builtin function in PHP and is used to sort an array such that array indices maintain their correlation with the array elements they are associated with, using a user-defined comparison function.

Syntax:

boolean uasort(array_name, user_defined_function);

Parameter: This function accepts two parameters and are described below:

1. array_name: This parameter represents the array which we need to sort.
2. user_defined_function: This is a comparator function and is used to compare values and sort the array. This function returns three types of values described below:
   • It return 0 when a=b
   • It return 1 when a>b and we want to sort input array in ascending order otherwise it will return -1 if we want to sort input array in descending order.
   • It return -1 when a<b and we want to sort input array in ascending order otherwise it will return 1 if we want to sort input array in descending order.

Return Value: It returns a boolean value, i.e. either TRUE on success and FALSE on failure.

Examples:

Input: array
       (
            "a" => 4,
            "b" => 2,
            "g" => 8,
            "d" => 6,
            "e" => 1,
            "f" => 9
       )
Output: Array 
        ( 
            [e] => 1 
            [b] => 2 
            [a] => 4 
            [d] => 6 
            [g] => 8 
            [f] => 9 
        )

Below programs illustrates the uasort() function in PHP:

• Sorting in ascending order: To sort the input array in ascending order, in the comparator function we will return 1 when a>b or -1 when a<b. Below program illustrates this:

  <?php
  // PHP program to sort in ascending
  // order using uasort() function
  
  // user_defined comparator function
  function sorting($a,$b)
  {
      if ($a==$b) return 0;
          return ($a<$b)?-1:1;
  }
  
  // input array
  $arr=array("a"=>4,"b"=>2,"g"=>8,"d"=>6,"e"=>1,"f"=>9);
  
  uasort($arr,"sorting");
  
  // printing sorted array.
  print_r($arr);
  
  ?>

  Output:

  Array
  (
      [e] => 1
      [b] => 2
      [a] => 4
      [d] => 6
      [g] => 8
      [f] => 9
  )
  

• Sorting in descending order: To sort the input array in descending order, in the comparator function we will return -1 when a>b or 1 when a<b. Below program illustrates this:

  <?php
  // PHP program to sort in descending
  // order using uasort() function
  
  // user_defined comparator function
  function sorting($a, $b)
  {
      if ($a == $b) return 0;
          return ($a > $b) ? -1 : 1;
  }
  
  // input array
  $input = array("d"=>"R", "a"=>"G", "b"=>"X", "f"=>"Z" );
  
  uasort($input, "sorting");
  
  // printing sorted array.
  print_r($input);
  
  ?>

  Output:

  Array
  (
      [f] => Z
      [b] => X
      [d] => R
      [a] => G
  )
  

Reference:
http://php.net/manual/en/function.uasort.php