in_array vs strpos for performance in php

As I often work with large datasets, I'd go with isset or !empty on an associative array and check for the key, like @Barmar suggests. Here is a quick 1M benchmark on an Intel® Core™ i3-540 (3.06 GHz)

$test = array("read", "edit", "delete", "admin");

echo "<pre>";

// --- strpos($rights,$test[$i%4]) ---

$rights = 'read,edit,delete,admin';
$mctime = microtime(true);
for($i=0; $i<=1000000; $i++) { if (strpos($rights,$test[$i%4]) !== false) { }}
echo '  strpos(... '.round(microtime(true)-$mctime,3)."s\n";

// --- in_array($test[$i%4],$rights) ---

$rights = array("read", "edit", "delete", "admin");
$mctime = microtime(true);
for($i=0; $i<=1000000; $i++) { if (in_array($test[$i%4],$rights)) { }}
echo 'in_array(... '.round(microtime(true)-$mctime,3)."s\n";

// --- !empty($rights[$test[$i%4]]) ---

$rights = array('read' => 1, 'edit' => 1, 'delete' => 1, 'admin' => 1);
$mctime = microtime(true);
for($i=0; $i<=1000000; $i++) { if (!empty($rights[$test[$i%4]])) { }}
echo '  !empty(... '.round(microtime(true)-$mctime,3)."s\n";

// --- isset($rights[$test[$i%4]]) ---

$rights = array('read' => 1, 'edit' => 1, 'delete' => 1, 'admin' => 1);
$mctime = microtime(true);
for($i=0; $i<=1000000; $i++) { if (isset($rights[$test[$i%4]])) { }}
echo '   isset(... '.round(microtime(true)-$mctime,3)."s\n\n";

echo "</pre>";

The winner is isset:

  strpos(... 0.393s
in_array(... 0.519s
  !empty(... 0.232s
   isset(... 0.209s

strpos is the fastest way to search a text needle, per the php.net documentation for strstr():

If you only want to determine if a particular needle occurs within haystack, use the faster and less memory intensive function strpos() instead.¹