如何根据PHP中的2个条件元素在多维数组中找到第一个和最后一个类似元素？

Question

我有一个多维数组，看起来像这样：

Array
(
    [event] => Array
        (
            [group] => 1
            [name] => Meetings
            [time] => Array
                (
                    [0] => Array
                        (
                            [room] => A
                            [label] => Meeting 100
                            [start] => 2016-09-07T14:30:00-04:00
                            [end] => 2016-09-07T15:00:00-04:00
                        )

                    [1] => Array
                        (
                            [room] => A
                            [label] => Meeting 100
                            [booking_start] => 2016-09-07T15:00:00-04:00
                            [booking_end] => 2016-09-07T15:30:00-04:00
                        )

                    [2] => Array
                        (
                            [room] => A
                            [label] => Meeting 200
                            [booking_start] => 2016-09-07T15:30:00-04:00
                            [booking_end] => 2016-09-07T16:00:00-04:00
                        )

                    [3] => Array
                        (
                            [room] => B
                            [label] => Meeting 300
                            [booking_start] => 2016-09-07T16:00:00-04:00
                            [booking_end] => 2016-09-07T16:30:00-04:00
                        )

                    [4] => Array
                        (
                            [room] => B
                            [label] => Meeting 300
                            [booking_start] => 2016-09-07T16:30:00-04:00
                            [booking_end] => 2016-09-07T17:00:00-04:00
                        )

                )

        )

)

每个“事件 - >时间”都有以1/2小时为增量列出的元素，导致会议跨越一个或多个阵列。我正在寻找一种有效的方法，根据“房间”和“标签”找到每个“时间”的第一个和最后一个实例，以便计算各个会议的开始和结束时间并返回“标签”， “房间”，实际开始时间和实际结束时间。任何人都可以提出一种可能运作良好的方法吗？