Question

1. What is the most efficient way to check if an array is a flat array of primitive values or if it is a multidimensional array?
2. Is there any way to do this without actually looping through an array and running is_array() on each of its elements?

Answer 1

The short answer is no you can’t do it without at least looping implicitly if the ‘second dimension’ could be anywhere. If it has to be in the first item, you’d just do

is_array($arr[0]); 

But, the most efficient general way I could find is to use a foreach loop on the array, shortcircuiting whenever a hit is found (at least the implicit loop is better than the straight for()):

$ more multi.php <?php  $a = array(1 => 'a',2 => 'b',3 => array(1,2,3)); $b = array(1 => 'a',2 => 'b'); $c = array(1 => 'a',2 => 'b','foo' => array(1,array(2)));  function is_multi($a) {     $rv = array_filter($a,'is_array');     if(count($rv)>0) return true;     return false; }  function is_multi2($a) {     foreach ($a as $v) {         if (is_array($v)) return true;     }     return false; }  function is_multi3($a) {     $c = count($a);     for ($i=0;$i<$c;$i++) {         if (is_array($a[$i])) return true;     }     return false; } $iters = 500000; $time = microtime(true); for ($i = 0; $i < $iters; $i++) {     is_multi($a);     is_multi($b);     is_multi($c); } $end = microtime(true); echo 'is_multi  took '.($end-$time).' seconds in $iters times\n';  $time = microtime(true); for ($i = 0; $i < $iters; $i++) {     is_multi2($a);     is_multi2($b);     is_multi2($c); } $end = microtime(true); echo 'is_multi2 took '.($end-$time).' seconds in $iters times\n'; $time = microtime(true); for ($i = 0; $i < $iters; $i++) {     is_multi3($a);     is_multi3($b);     is_multi3($c); } $end = microtime(true); echo 'is_multi3 took '.($end-$time).' seconds in $iters times\n'; ?>  $ php multi.php is_multi  took 7.53565130424 seconds in 500000 times is_multi2 took 4.56964588165 seconds in 500000 times is_multi3 took 9.01706600189 seconds in 500000 times 

Implicit looping, but we can’t shortcircuit as soon as a match is found…

$ more multi.php <?php  $a = array(1 => 'a',2 => 'b',3 => array(1,2,3)); $b = array(1 => 'a',2 => 'b');  function is_multi($a) {     $rv = array_filter($a,'is_array');     if(count($rv)>0) return true;     return false; }  var_dump(is_multi($a)); var_dump(is_multi($b)); ?>  $ php multi.php bool(true) bool(false)