Removing a value from an associative array

Is there any way I can remove a key/value pair from an associative array, given the key?

unset() -

$arr['keep_this_1'] = 'I want 1';
$arr['remove_this'] = 'this will be gone';
$arr['keep_this_2'] = 'I want 2';

echo "<pre>";
print_r($arr);
echo "</pre>";
echo "<br />";

$key = 'remove_this';
unset($arr[$key]);

echo "<pre>";
print_r($arr);
echo "</pre>";