public function getBy($index, $nested = false) {
		$out = array();
		foreach ($this->getArrayCopy() as $model)
			if ($model->exists($index)) {
				$val = $model->get($index, true);
				if (!empty($val))
					if($nested) $out[(string) $val][] = $model;
					else        $out[(string) $val] = $model;
			}
		return $out;
	}