php fastest array lookup

If you use arrays in PHP, one of the most common tasks you’ll find yourself doing is determining if Item A is in Array X. The function you would probably use in this case is PHP’s in_array.

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1	bool in_array ( mixed $needle , array $haystack [, bool $strict = FALSE ] )

This function works great and I recommend sticking to it when it makes sense. However, when you’re dealing with a very large haystack and need to run in_array() on thousands of values, you’ll discover that in_array isn’t particularly fast when cumulated over thousands of calls. Having recently run into this situation, I set up a little experiment to try two different approaches to in_array().

The haystack in my experiment was an array containing 60,000 strings that were 50 characters in length as values.

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1	$arr = array("String1","String2","String3", etc...)

The needle was a string of 50 characters.

Method A – Using in_array()

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if (in_array($needle, $haystack)) {     echo("Method A : needle " . $needle . " found in haystack<BR>"); }

Method B – Using isset()
Basically, I reformatted the haystack so that the values of my original array became keys instead and the new value for each key was set to 1.

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1 2	foreach(array_values($haystack) as $v)     $new_haystack[$v] = 1;

So my haystack became :

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$arr["String1"] = 1; $arr["String2"] = 1; $arr["String3"] = 1; etc.

Then, all you need to do is look up the key:

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if (isset($haystack[$needle])) {     echo("Method B : needle " . $needle . " found in haystack<BR>"); }

Method C – Using array_intersect()
When all you really need to know is if needle is in haystack, using array_intersect() can also work.

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if (count(array_intersect(array($needle), $haystack))>0) {     echo("Method C : needle " . $needle . " found in haystack<BR>"); }

With these different methods in place, I executed them against the same $haystack and $needle and the results were clear :

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Method A : 0.003180980682373 seconds Method B : 0.0000109672546 seconds Method C : 0.045687913894653 seconds

Method B wins! Keep in mind that this only really becomes interesting with very large data sets. For those of you wondering how long it took to re-arrange the haystack for Method B to use, the answer is0.025528907775879 seconds.

In this experiment, determining if 100,000 strings are or are not in the data set went from 318.098 seconds with in_array() to 1.1222 seconds using isset(). That’s pretty decent.