gistfile1.php

<?php

	/**
	 * Applys a function to a specific set of keys in an array
	 * 
	 * @param array & $source_array the array to apply the callback to
	 *
	 * @return null
	 */
	public function apply( & $source_array, $callback, $keys)
	{
		if (true === $keys)
		{
			array_walk($source_array, $callback);
		}
		else
		{
			foreach ($keys as $key)
			{
				$source_array[$key] = call_user_func($callback, $source_array[$key]);
			}
		}
	}