Normalize the case of array keys in PHP

Question

Is there a "better" way (built-in function, better algorithm) to normalize the case of all the keys in a PHP array? Looping though and creating a new array works

$new = array();
foreach( $old as $key=>$value) {
    $key = strToLower($key);
    if(!array_key_exists($key,$new) {
        $new[$key] = $value;
    } 
    else {
        throw new Exception('Duplicate Key Encountered');
    }

}

but it seems like these should be a way to do this "in place".

Update: It looks like there is a built in, the not deceptively named yet somehow missed by me array_change_key_case. I'd still be interesting in seeing algorithmic approaches that would let you better handle what happens when you hit "duplicate" keys.

Answer 1

I believe array_change_key_case does what you're looking for.

http://us3.php.net/manual/en/function.array-change-key-case.php

Answer 2

I found that builtin functions are much faster than loops when processing large arrays. This might do what you want (untested code):

$lowerCaseKeys = array_map('strtolower', array_keys($array));
$duplicates = array_filter(array_count_values($lowerCaseKeys), create_function('$count', 'return $count > 1;'));
if (!empty($duplicates)) {
    throw new Exception('duplicate keys found: ' . implode(',', array_keys($duplicates)));
}
# Recreate the array with lower-case keys
$array = array_combine($lowerCaseKeys, array_values($array));

EDIT Or the pragmatic approach (should be much faster):

$lowerCaseKeyArray = array_change_key_case($array);
if (count($lowerCaseKeyArray) !== count($array)) {
    # You can extract the duplicate keys here as above, if you like
    throw new Exception('duplicate keys found!');
}