PHP array_flip() Function

This built-in function of PHP is used to exchange elements within an array, i.e., exchange all keys with their associated values in an array and vice-versa. We must remember that the values of the array need to be valid keys, i.e. they need to be either integer or string. A warning will be thrown if a value has the wrong type, and the key/value pair in question will not be included in the result.

Examples:

Input : array = ("aakash" => 20, "rishav" => 40, "gaurav" => 60)
Output:
        Array
        (
          [20] => aakash
          [40] => rishav
          [60] => gaurav
        )
Explanation: The keys and values are exchanged and the last key or value is taken.

Input : array = ("aakash" => "rani", "rishav" => "sristi", 
                 "gaurav" => "riya", "laxman" => "rani")
Output:
        Array
        (
          [rani] => laxman
          [sristi] => rishav
          [riya] => gaurav
        )

Syntax:

array array_flip($array)

Parameters: The function takes only one parameter $array that refers to the input array.

Return Type: This function returns another array, with the elements exchanged or flipped, it returns null if the input array is invalid.

Below program illustrates the working of array_flip() function in PHP:
Example 1:

<?php

// PHP function to illustrate the use of array_flip()
function Flip($array)
{
    $result = array_flip($array);
    return($result);
}

$array = array("aakash" => "rani", "rishav" => "sristi",
               "gaurav" => "riya", "laxman" => "rani");
print_r(Flip($array));

?>

Output:

Array
(
    [rani] => laxman
    [sristi] => rishav
    [riya] => gaurav
)

If multiple values in the array are the same, then on the use of the array_flip() function, only the key with the maximum index (after swap) will be added to the array. (This is done to ensure that no keys have duplicates.)

Example 2:

<?php
// PHP program to array_flip() with multiple similar values

//function to use array_flip()
function Flip($array)
{
    $result = array_flip($array);
    return($result);
}


//make the array
$array = array("a" => 1, "b" => 1, "c" => 2);

//print all resultant values
print_r(Flip($array));

?>

Output:

Array
(
    [1] => b
    [2] => c
)

References: http://php.net/manual/en/function.array-flip.php