php man page for array_diff_key

ARRAY_DIFF_KEY(3)							 1							 ARRAY_DIFF_KEY(3)

array_diff_key - Computes the difference of arrays using keys for comparison

SYNOPSIS
       array array_diff_key (array  $array1, array  $array2, [array  $...])

DESCRIPTION
	Compares  the  keys  from $array1 against the keys from $array2 and returns the difference. This function is like array_diff(3) except the
       comparison is done on the keys instead of the values.

PARAMETERS
	      o $array1
		- The array to compare from

	      o $array2
		- An array to compare against

	      o $...
		- More arrays to compare against

RETURN VALUES
	Returns an array containing all the entries from $array1 whose keys are not present in any of the other arrays.

EXAMPLES
       Example #1

	      array_diff_key(3) example

	       The two keys from the key => value pairs are considered equal only if (string) $key1 === (string) $key2 . In other words  a  strict
	      type check is executed so the string representation must be the same.

	      <?php
	      $array1 = array('blue'  => 1, 'red'  => 2, 'green'  => 3, 'purple' => 4);
	      $array2 = array('green' => 5, 'blue' => 6, 'yellow' => 7, 'cyan'	 => 8);

	      var_dump(array_diff_key($array1, $array2));
	      ?>

	      The above example will output:

	      array(2) {
		["red"]=>
		int(2)
		["purple"]=>
		int(4)
	      }

NOTES
       Note

	       This  function  only  checks  one  dimension  of  a  n-dimensional  array.  Of  course  you  can  check	deeper dimensions by using
	      array_diff_key($array1[0], $array2[0]);.

SEE ALSO
       array_diff(3), array_udiff(3), array_diff_assoc(3), array_diff_uassoc(3), array_udiff_assoc(3), array_udiff_uassoc(3),  array_diff_ukey(3),
       array_intersect(3), array_intersect_assoc(3), array_intersect_uassoc(3), array_intersect_key(3), array_intersect_ukey(3).

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