Pandas中具有重复索引且没有聚合函数的透视表

我有一个数据帧:

    device_id   timestamp             metric_id    value
0   device_1    2020-12-04 05:15:00   cpu_5min      116
1   device_1    2020-12-04 05:30:00   cpu_5min      213
2   device_1    2020-12-04 05:35:00   cpu_5min      427
3   device_1    2020-12-04 05:15:00   vol_max       734
4   device_1    2020-12-04 05:30:00   vol_max       325
5   device_1    2020-12-04 05:35:00   vol_max       668
6   device_2    2020-12-04 05:15:00   cpu_5min      540
7   device_2    2020-12-04 05:30:00   cpu_5min      127
8   device_2    2020-12-04 05:35:00   cpu_5min      654

我需要把这张桌子转成这样:

    device_id   timestamp              cpu_5min   vol_max
0   device_1    2020-12-04 05:15:00      116        734
1   device_1    2020-12-04 05:30:00      213        325
2   device_1    2020-12-04 05:35:00      427        668
3   device_2    2020-12-04 05:15:00      540        NA
4   device_2    2020-12-04 05:30:00      127        NA
5   device_2    2020-12-04 05:35:00      654        NA

我已经看了SO上的其他pivot答案,但它们似乎都假定有一个聚合函数和/或非重复索引。