PHP case-insensitive in_array function

Question

The obvious thing to do is just convert the search term to lowercase:

if (in_array(strtolower($word), $array)) { 
  ...

of course if there are uppercase letters in the array you'll need to do this first:

$search_array = array_map('strtolower', $array);

and search that. There's no point in doing strtolower on the whole array with every search.

Searching arrays however is linear. If you have a large array or you're going to do this a lot, it would be better to put the search terms in key of the array as this will be much faster access:

$search_array = array_combine(array_map('strtolower', $a), $a);

then

if ($search_array[strtolower($word)]) { 
  ...

The only issue here is that array keys must be unique so if you have a collision (eg "One" and "one") you will lose all but one.

function in_arrayi($needle, $haystack) {
    return in_array(strtolower($needle), array_map('strtolower', $haystack));
}

From Documentation

you can use preg_grep():

$a= array(
 'one',
 'two',
 'three',
 'four'
);

print_r( preg_grep( "/ONe/i" , $a ) );

function in_arrayi($needle, $haystack) {
    return in_array(strtolower($needle), array_map('strtolower', $haystack));
}

Source: php.net in_array manual page.

Say you want to use the in_array, here is how you can make the search case insensitive.

Case insensitive in_array():

foreach($searchKey as $key => $subkey) {

     if (in_array(strtolower($subkey), array_map("strtolower", $subarray)))
     {
        echo "found";
     }

}

Normal case sensitive:

foreach($searchKey as $key => $subkey) {

if (in_array("$subkey", $subarray))

     {
        echo "found";
     }

}