(PHP 4, PHP 5, PHP 7)
array_flip — Exchanges all keys with their associated values in an array
$array
   )
   array_flip() returns an array in flip
   order, i.e. keys from array become values and values
   from array become keys.
  
   Note that the values of array need to be valid
   keys, i.e. they need to be either integer or
   string. A warning will be emitted if a value has the wrong
   type, and the key/value pair in question will not be included
   in the result.
  
If a value has several occurrences, the latest key will be used as its value, and all others will be lost.
arrayAn array of key/value pairs to be flipped.
   Returns the flipped array on success and NULL on failure.
  
Example #1 array_flip() example
<?php
$input = array("oranges", "apples", "pears");
$flipped = array_flip($input);
print_r($flipped);
?>
The above example will output:
Array
(
    [oranges] => 0
    [apples] => 1
    [pears] => 2
)
Example #2 array_flip() example : collision
<?php
$input = array("a" => 1, "b" => 1, "c" => 2);
$flipped = array_flip($input);
print_r($flipped);
?>
The above example will output:
Array
(
    [1] => b
    [2] => c
)