Trying to understand array_diff_uassoc optimization

Question

It seems that arrays sorted before comparing each other inside array_diff_uassoc.

What is the benefit of this approach?

Test script

functio         


        

Answer 1

Sorting algorithm didn't change in PHP 7. Elements are just passed in another order to the sorting algorithm for some performance improvements.

Well, benefit could be an eventual faster execution. You really hit worst case when both arrays have completely other keys.

Worst case complexity is twice sorting the arrays and then comparisons of each key of the two arrays. O(n*m + n * log(n) + m * log(m))

Best case is twice sorting and then just as many comparisons as there are elements in the smaller array. O(min(m, n) + n * log(n) + m * log(m))

In case of a match, you wouldn't have to compare against the full array again, but only from the key after the match on.

But in current implementation, the sorting is just redundant. Implementation in php-src needs some improvement I think. There's no outright bug, but implementation is just bad. If you understand some C: http://lxr.php.net/xref/PHP_TRUNK/ext/standard/array.c#php_array_diff (Note that that function is called via php_array_diff(INTERNAL_FUNCTION_PARAM_PASSTHRU, DIFF_ASSOC, DIFF_COMP_DATA_INTERNAL, DIFF_COMP_KEY_USER); from array_diff_uassoc)