PHP: in_array() and multidimensional array

in_array() does not work on multidimensional arrays. You could write a recursive function to do that for you:

function in_array_r($needle, $haystack) {
    $found = false;

    foreach ($haystack as $item) {
        if ($item == $needle) {
            $found = true;
            break;
        } elseif (is_array($item)) {
            $found = in_array_r($needle, $item);
        }
    }

    return $found;
}

Usage:

$b = array(array("Mac", "NT"), array("Irix", "Linux"));
if (in_array_r("Irix", $b)) {
    echo 'found';
} else {
    echo 'not found';
}

This is the first function of this type that I found in the php manual for in_array. Functions in the comment sections aren't always the best but if it doesn't do the trick you can look in there too :)

<?php
function in_multiarray($elem, $array)
    {
        // if the $array is an array or is an object
         if( is_array( $array ) || is_object( $array ) )
         {
             // if $elem is in $array object
             if( is_object( $array ) )
             {
                 $temp_array = get_object_vars( $array );
                 if( in_array( $elem, $temp_array ) )
                     return TRUE;
             }

             // if $elem is in $array return true
             if( is_array( $array ) && in_array( $elem, $array ) )
                 return TRUE;


             // if $elem isn't in $array, then check foreach element
             foreach( $array as $array_element )
             {
                 // if $array_element is an array or is an object call the in_multiarray function to this element
                 // if in_multiarray returns TRUE, than return is in array, else check next element
                 if( ( is_array( $array_element ) || is_object( $array_element ) ) && $this->in_multiarray( $elem, $array_element ) )
                 {
                     return TRUE;
                     exit;
                 }
             }
         }

         // if isn't in array return FALSE
         return FALSE;
    }
?>

This will do it:

foreach($b as $value)
{
    if(in_array("Irix", $value))
    {
        echo "Got Irix";
    }
}

in_array only operates on a one dimensional array, so you need to loop over each sub array and run in_array on each.

As others have noted, this will only for for a 2-dimensional array. If you have more nested arrays, a recursive version would be better. See the other answers for examples of that.