python - 添加额外的列作为累积时间差

Question

如何添加一个额外的列，即每门类(class)的时间差累计值？例如初始表为:

 id_A       course     weight                ts_A       value
 id1        cotton     3.5       2017-04-27 01:35:30  150.000000
 id1        cotton     3.5       2017-04-27 01:36:00  416.666667
 id1        cotton     3.5       2017-04-27 01:36:30  700.000000
 id1        cotton     3.5       2017-04-27 01:37:00  950.000000
 id2     cotton blue   5.0       2017-04-27 02:35:30  150.000000
 id2     cotton blue   5.0       2017-04-27 02:36:00  450.000000
 id2     cotton blue   5.0       2017-04-27 02:36:30  520.666667
 id2     cotton blue   5.0       2017-04-27 02:37:00  610.000000

预期的结果是:

 id_A       course     weight                ts_A       value      cum_delta_sec
 id1        cotton     3.5       2017-04-27 01:35:30  150.000000      0
 id1        cotton     3.5       2017-04-27 01:36:00  416.666667      30 
 id1        cotton     3.5       2017-04-27 01:36:30  700.000000      60
 id1        cotton     3.5       2017-04-27 01:37:00  950.000000      90
 id2     cotton blue   5.0       2017-04-27 02:35:30  150.000000      0
 id2     cotton blue   5.0       2017-04-27 02:36:00  450.000000      30
 id2     cotton blue   5.0       2017-04-27 02:36:30  520.666667      60
 id2     cotton blue   5.0       2017-04-27 02:37:00  610.000000      90

Answer 1

您可以将 diff 方法与 cumsum 链接起来:

# convert ts_A to datetime type
df.ts_A = pd.to_datetime(df.ts_A)

# convert ts_A to seconds, group by id and then use transform to calculate the cumulative difference
df['cum_delta_sec'] = df.ts_A.astype(int).div(10**9).groupby(df.id_A).transform(lambda x: x.diff().fillna(0).cumsum())
df