note 78573 deleted from function.array-diff by danbrown

Note Submitter: Hayley Watson ---- A wee idiom for KEEPING only those elements of an array $a that appear in an array $b (without introducing any elements of $b that do not appear in $a). <?php array_diff($a, array_diff($a, $b)) ?> And for mr dot kschan at gmail dot com: if it's the SYMMETRIC difference you want, (A-B typically is not equal to B-A; consider the case when A and B are integers), there is Viking Coder's comment 04-Jan-2006, or there is the alternative: <?php function symmetric_array_diff($array1, $array2) { return array_diff(array_merge($array1, $array2), array_intersect($array1, $array2)); } ?> Viking Coder's expression and mine are equivalent: (A-B)u(B-A) == (AuB)-(AnB). They're probably about equal in efficiency.