Question

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What’s quicker and better to determine if an array key exists in PHP?

suppose I want to store the list of friends I have on memcache.
sometimes i need to search if a user is on my list and sometime i need to fetch all the list of friends.

would you rather

$friends[] = $friend

or

$friends[$friend] = 1;

the rationale is to save as much as ram as decently possible without penalizing speed.
I didn’t find any case study for php 5.3.8 that can help me on my little dilemma:
under load, which is faster to perform?

array_key_exists or in_array? (ie: is foo a friend of bar?)

Also, sometimes i need to fetch the whole list of friends so i need to iterate the whole list in order to build an array of friends. not sure at all about the second method, since I don’t know yet if there will be more array_search|array_key_exists|in_array or fetch of full friends list.

any idea?

Answer 1

array_key_exists is much faster. array_search must traverse the whole array, so it is O(n). array_key_exists is a hash table lookup, so it is O(1).

See http://en.wikipedia.org/wiki/Big_O_notation if you are new to this concept.

Between array_key_exists and isset, though both are very fast [O(1)], isset is significantly faster. If this check is happening many thousands of times, you’d want to use isset.

It should be noted that they are not identical, though — when the array key exists but the value is null, isset will return false and array_key_exists will return true. If the value may be null, you need to use array_key_exists.