如何在mongodb聚合中获得嵌套数组的总和？

Question

My Array就是这样，

[data] =＆gt;排列                 （                     [0] =＆gt;排列                         （                             [test] =＆gt; 164.765                         ）

                [1] => Array
                    (
                        [test] => 26.1
                    )

                [2] => Array
                    (
                        [test] => 194.564
                    )

                [3] => Array
                    (
                        [test] => 54
                    )

                [4] => Array
                    (
                        [test] => 99.753
                    )

                [5] => Array
                    (
                        [test] => 32.735
                    )

                [6] => Array
                    (
                        [test] => 2715.865
                    )

                [7] => Array
                    (
                        [test] => 94.595
                    )
            )

通过使用$ sum我一直得到0。有没有办法得到这个数组的总和？