如何获得微秒秒的cumsum值？
它低于输入数据
time A B
2018-04-04 00:01:52.474 0.0 0.0
2018-04-04 00:01:52.676 0.0 0.0
2018-04-04 00:01:52.692 0.0 0.0
2018-04-04 00:01:52.754 1.0 0.0
2018-04-04 00:01:52.817 1.0 0.0
2018-04-04 00:01:52.848 1.0 0.0
2018-04-04 00:01:52.895 1.0 0.0
2018-04-04 00:01:53.051 1.0 0.0
2018-04-04 00:01:53.082 1.0 0.0
2018-04-04 00:01:53.160 1.0 0.0
2018-04-04 00:01:53.316 1.0 1.0
2018-04-04 00:01:53.332 1.0 1.0
输出数据：
我想在数据帧
中获取字符时间获取值time A B cumsum_Time
2018-04-04 00:01:52.474 0.0 0.0 NaN
2018-04-04 00:01:52.676 0.0 0.0 NaN
2018-04-04 00:01:52.692 0.0 0.0 NaN
2018-04-04 00:01:52.754 1.0 0.0 0.0
2018-04-04 00:01:52.817 1.0 0.0 0.04~
2018-04-04 00:01:52.848 1.0 0.0 0.09~
2018-04-04 00:01:52.895 1.0 0.0 0.14~
2018-04-04 00:01:53.051 1.0 0.0 0.32~
2018-04-04 00:01:53.082 1.0 0.0 0.35~
2018-04-04 00:01:53.160 1.0 0.0 0.43~
2018-04-04 00:01:53.316 1.0 1.0 0.52~
2018-04-04 00:01:53.332 1.0 1.0 NaN
...
输出2更改值
2018/04/04 00:01:52:754 1.0 0.0 NaN 0 this1
2018/04/04 00:01:52:817 1.0 0.0 1 0.06
2018/04/04 00:01:52:848 1.0 0.0 1 0.09
2018/04/04 00:01:52:895 1.0 0.0 1 0.14
2018/04/04 00:01:53:051 1.0 0.0 1 0.303
2018/04/04 00:01:53:082 1.0 0.0 1 0.323
2018/04/04 00:01:53:160 1.0 0.0 1 0.415
2018/04/04 00:01:53:316 1.0 1.0 1 0.562 this2