DataSet::filterByField

protected function filterByField($field, $value)
{
	$result = array();
	foreach ($this->values as $item)
	{
		if ($value === null && !array_key_exists($field, $item))
		{
			continue;
		}
		elseif (!isset($item[$field]) && $value !== null)
		{
			continue;
		}

		if ((string)$item[$field] === (string)$value)
		{
			$result[] = $item;
		}
	}

	return new static($result);
}