Courses::getGroupCourseProgress( $courseId = null )

	public function getGroupCourseProgress($courseId = null)
	{
		if (! $courseId) {
			$courseId = get_the_ID();
		}

		$members    = groups_get_group_members();
		$totalSteps = learndash_get_course_steps_count($courseId);

		if ($members['count'] == 0) {
			return 0;
		}

		if ($totalSteps == 0) {
			return 0;
		}

		$totalSteps  = learndash_get_course_steps_count($courseId);
		$memberSteps = array_sum(array_map(function($member) use ($courseId) {
			return learndash_course_get_completed_steps($member->id, $courseId);
		}, $members['members']));

		return round($memberSteps / ($members['count'] * $totalSteps) * 100);
	}