PHP: returning an array of single attributes from an array of objects

I miss Ruby’s shorthand collect method to return an array of single attributes:

animals.collect(&:name)

…so I’ve created a (less elegant) equivalent for PHP.

class ArrayExtensions
{
    /**
     * From an array of objects, create a new array containing only 
     * a single attribute of each object
     * 
     * Similar to array.collect(&:attribute) in Ruby
     */
    public static function collect_by_attribute($attribute, $array_of_objects)
    {
        if (!is_array($array_of_objects))
        {
            return array();
        }

        $output = array();

        foreach ($array_of_objects as $object)
        {
            if (is_object($object) && isset($object->$attribute))
            {
                $output[] = $object->$attribute;
            }
        } 
        
        return $output;
    }
}

Use it like this:

$colours = ArrayExtensions::collect_by_attribute('colour', $animals);

…and you’ll get a simple array containing just the attribute you’ve specified:

array('brown', 'blue', 'green')

Update

If you happen to be using PHP ActiveRecord, they have a function called collect that will accomplish the same thing.

$colours = ActiveRecord\collect($animals, 'colour');