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copied!<p>Note that as RoBorg pointed out, there's overhead in creating the array so it should be moved inside the iteration loop. For this reason, Sparr's post is also a little misleading as there's overhead with the array_flip function.</p> <p>Here's another example with all 5 variations:</p> <pre><code>$array = array('test1', 'test2', 'test3', 'test4'); $var = 'test'; $iterations = 1000000; $start = microtime(true); for($i = 0; $i < $iterations; ++$i) { if ($var != 'test1' && $var != 'test2' && $var != 'test3' && $var != 'test4') {} } print "Time1: ". (microtime(true) - $start); $start = microtime(true); for($i = 0; $i < $iterations; ++$i) { if (!in_array($var, $array) ) {} } print "Time2: ".(microtime(true) - $start); $start = microtime(true); for($i = 0; $i < $iterations; ++$i) { if (!in_array($var, array('test1', 'test2', 'test3', 'test4')) ) {} } print "Time2a: ".(microtime(true) - $start); $array2 = array_flip($array); $start = microtime(true); for($i = 0; $i < $iterations; ++$i) { if (!isset($array2[$var])) {} } print "Time3: ".(microtime(true) - $start); $start = microtime(true); for($i = 0; $i < $iterations; ++$i) { $array2 = array_flip($array); if (!isset($array2[$var])) {} } print "Time3a: ".(microtime(true) - $start); </code></pre> <p>My results:</p> <pre><code>Time1 : 0.59490108493 // straight comparison Time2 : 0.83790588378 // array() outside loop - not accurate Time2a: 2.16737604141 // array() inside loop Time3 : 0.16908097267 // array_flip outside loop - not accurate Time3a: 1.57209014893 // array_flip inside loop </code></pre> <p>In summary, using <code>array_flip</code> (with isset) is faster than inarray but not as fast as a straight comparison.</p>

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