The PHP array_flip() Function And Detecting Functions

The array_flip() function in PHP is used to swap the values of an array with the keys. Take the following array.

$array = array('key1'=>'value1', 'key2'=>'value2');

To exchange all the values with the keys we pass it through the array_flip() function.

$array = array_flip($array);


echo ''.print_r($array, true).'';

This prints out the following:

Array


(


 [value1] => key1


 [value2] => key2


)

If any of the values are the same then the highest key is overwritten. The following array:

$array = array('a', 'a', 'a', 'b');

Will produce the following array when passed through array_flip().

Array


(


 [a] => 2


 [b] => 3


)

If this bit of code is essential to the running of your program you can make sure that it exists by using the function_exists() function. This function takes a single parameter, which is the name of the function you are testing for as a string. The following code checks to see if the array_flip() function exists, and if not defines a version that works in the same way.

if ( !function_exists('array_flip') ) {


 function array_flip($array){


  $values = array();


  while ( list($key, $val) = each($array) ) {


    $values[$val] = $key;


  }


  return $values;


 }


}

The array_flip() function was included in PHP version 4, so you only need to do this if you expect someone to try and run your code on a very old version of PHP. However, there are many new fucntions included with PHP 5 that you might want to check for when writing code.