PHP: in_array() vs array_intersect() performance

Question

What, and how much, is faster - manually iterating over an array with foreach and checking for needle occurrence with in_array(), or using array_intersect()?

this answer might helpful for you : stackoverflow.com/questions/6329211/… — Mahdi Rashidi
– Mahdi Rashidi, Commented Oct 31, 2016 at 4:27

Community · Accepted Answer · 2020-06-20 09:12:55Z

11

Benchmark

Test Script

<?php
$numbers = range(32, 127);
$numbersLetters = array_map('chr', $numbers);

for (;;) {
    $numbersLetters = array_merge($numbersLetters, $numbersLetters);

    if (count($numbersLetters) > 10000) {
        break;
    }
}

$numbers = range(1, count($numbersLetters));

printf("Sample size: %d elements in 2 arrays (%d total) \n", count($numbers), count($numbers) + count($numbersLetters));
printf("Benchmarking speed in foreach + in_array() scenario... (this might take a while) ");

shuffle($numbers);
shuffle($numbersLetters);

$t1 = microtime(true);

foreach ($numbers as $number) {
    if (in_array($number, $numbersLetters)) {}
}

$t2 = microtime(true);

printf("DONE!\n");
printf("Time elapsed: %.5f \n", $t2 - $t1);

// =============================------------===============================

printf("Benchmarking speed with array_intersect...");

shuffle($numbers);
shuffle($numbersLetters);

$t1 = microtime(true);

array_intersect($numbers, $numbersLetters);

$t2 = microtime(true);

printf("DONE!\n");
printf("Time elapsed: %.5f \n", $t2 - $t1);

Output

Sample size: 12288 elements in 2 arrays (24576 total) 
Benchmarking speed in foreach + in_array() scenario... (this might take a while) DONE!
Time elapsed: 3.79213 
Benchmarking speed with array_intersect...DONE!
Time elapsed: 0.05765

Fiddle: http://ideone.com/OZ2Idf

Conclusion

array_intersect is much faster than foreach + in_array.

Why is `array_intersect` faster?

The intersection is computed in C code, as opposed to PHP
Internally, Zend engine sorts the array prior to computing the intersection (why is processing a sorted array faster?)

edited Jun 20, 2020 at 9:12

CommunityBot

11 silver badge

answered Oct 30, 2016 at 16:56

onin

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2 Comments

Rafał Łyczkowski Over a year ago

Update including codedmemes.com/lib/best-performance-array-intersection would be nice here

Markus AO Over a year ago

Fast forward to PHP 8.2 and the difference is a small order of magnitude greater still. foreach + in_array(): 5.11544, array_intersect: 0.01294.

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