core-bundle/src/Resources/contao/dca/tl_page.php
public function getPageLayouts()
	{
		$objLayout = $this->Database->execute("SELECT l.id, l.name, t.name AS theme FROM tl_layout l LEFT JOIN tl_theme t ON l.pid=t.id ORDER BY t.name, l.name");

		if ($objLayout->numRows < 1)
		{
			return array();
		}

		$return = array();

		while ($objLayout->next())
		{
			$return[$objLayout->theme][$objLayout->id] = $objLayout->name;
		}

		return $return;
	}
public function getPageLayouts()
	{
		$objLayout = $this->Database->execute("SELECT l.id, l.name, t.name AS theme FROM tl_layout l LEFT JOIN tl_theme t ON l.pid=t.id ORDER BY t.name, l.name");

		if ($objLayout->numRows < 1)
		{
			return array();
		}

		$return = array();

		while ($objLayout->next())
		{
			$return[$objLayout->theme][$objLayout->id] = $objLayout->name;
		}

		return $return;
	}
Return all page layouts grouped by theme

@return array