what is faster: in_array or isset? [closed]

Question

This question is merely for me as I always like to write optimized code that can run also on cheap slow servers (or servers with A LOT of traffic)

I looked around and I was not able to find an answer. I was wondering what is faster between those two examples keeping in mind that the array's keys in my case are not important (pseudo-code naturally):

<?php $a = array(); while($new_val = 'get over 100k email addresses already lowercased'){     if(!in_array($new_val, $a){         $a[] = $new_val;         //do other stuff     } } ?>  <?php $a = array(); while($new_val = 'get over 100k email addresses already lowercased'){     if(!isset($a[$new_val]){         $a[$new_val] = true;         //do other stuff     } } ?> 

As the point of the question is not the array collision, I would like to add that if you are afraid of colliding inserts for $a[$new_value], you can use $a[md5($new_value)]. it can still cause collisions, but would take away from a possible DoS attack when reading from an user provided file (http://nikic.github.com/2011/12/28/Supercolliding-a-PHP-array.html)

Answer 1

The answers so far are spot-on. Using isset in this case is faster because

• It uses an O(1) hash search on the key whereas in_array must check every value until it finds a match.
• Being an opcode, it has less overhead than calling the in_array built-in function.

These can be demonstrated by using an array with values (10,000 in the test below), forcing in_array to do more searching.

isset:    0.009623 in_array: 1.738441 

This builds on Jason's benchmark by filling in some random values and occasionally finding a value that exists in the array. All random, so beware that times will fluctuate.

$a = array(); for ($i = 0; $i < 10000; ++$i) {     $v = rand(1, 1000000);     $a[$v] = $v; } echo "Size: ", count($a), PHP_EOL;  $start = microtime( true );  for ($i = 0; $i < 10000; ++$i) {     isset($a[rand(1, 1000000)]); }  $total_time = microtime( true ) - $start; echo "Total time: ", number_format($total_time, 6), PHP_EOL;  $start = microtime( true );  for ($i = 0; $i < 10000; ++$i) {     in_array(rand(1, 1000000), $a); }  $total_time = microtime( true ) - $start; echo "Total time: ", number_format($total_time, 6), PHP_EOL; 

Answer 2

Which is faster: isset() vs in_array()

isset() is faster.

While it should be obvious, isset() only tests a single value. Whereas in_array() will iterate over the entire array, testing the value of each element.

Rough benchmarking is quite easy using microtime().

Results:

Total time isset():    0.002857 Total time in_array(): 0.017103 

Note: Results were similar regardless if existed or not.

Code:

<?php $a = array(); $start = microtime( true );  for ($i = 0; $i < 10000; ++$i) {     isset($a['key']); }  $total_time = microtime( true ) - $start; echo "Total time: ", number_format($total_time, 6), PHP_EOL;  $start = microtime( true );  for ($i = 0; $i < 10000; ++$i) {     in_array('key', $a); }  $total_time = microtime( true ) - $start; echo "Total time: ", number_format($total_time, 6), PHP_EOL;  exit; 

Additional Resources

I'd encourage you to also look at:

• PHP Benchmark
• PHPPerf
• XDebug