(PHP 4, PHP 5)
array_flip — Exchanges all keys with their associated values in an array
$trans
   )
   array_flip() returns an array in flip
   order, i.e. keys from trans become values and values
   from trans become keys.
  
   Note that the values of trans 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 values, and all others will be lost.
transAn array of key/value pairs to be flipped.
   Returns the flipped array on success and NULL on failure.
  
Example #1 array_flip() example
<?php
$trans = array_flip($trans);
$original = strtr($str, $trans);
?>
Example #2 array_flip() example : collision
<?php
$trans = array("a" => 1, "b" => 1, "c" => 2);
$trans = array_flip($trans);
print_r($trans);
?>
now $trans is:
Array
(
    [1] => b
    [2] => c
)