Alternative implementation of in_array using either isset or array_key_exists. This approach requires restructuring the original array.

in-array-optimizations.php

<?php
	//This isset optimization is not suitable for arrays that contains null values.
	/*
		$a = array('a' => null);
		isset($a['a']); // Will be FALSE
		array_key_exists('a', $a); // Will be TRUE	
	*/
	
	$total = 10000;
	$paragraph = 'this is a sentence. Crud! $$$$!';
	$words = explode(' ', $paragraph);

	// Create a bunch of letter entries
	$sequence = [];

	for ($j = 0; $j < 10000; $j++) {
	    $sequence[] = 'a' . $j;
	}

	$s = microtime(true);

	for ($j = 0; $j < $total; $j++) {
	    foreach ($words as $word) {
		in_array(strtolower($word), $sequence);
	    }
	}
	echo "in_array: " . (microtime(true) - $s) . "\n";

	// Convert the array to a hash
	$hash = array_fill_keys($sequence, true);
	$s = microtime(true);

	for ($j = 0; $j < $total; $j++) {
	    foreach ($words as $word) {
		isset($hash[strtolower($word)]);
	    }
	}

	echo "isset:     " . (microtime(true) - $s) . "\n";

	$s = microtime(true);

	for ($j = 0; $j < $total; $j++) {
	    foreach ($words as $word) {
		array_key_exists(strtolower($word), $hash);
	    }
	}

	echo "array_key_exists:     " . (microtime(true) - $s) . "\n";

Since you have two arrays, you could use the array_intersect instead of a foreach loop?

Since you have two arrays, you could use the array_intersect instead of a foreach loop?

Thanks