在组内使用pandas.shift() [英] Use pandas.shift() within a group

问题描述

我有一个包含面板数据的数据框，比方说这是100个不同对象的时间序列:

I have a dataframe with panel data, let's say it's time series for 100 different objects:

object  period  value 
1       1       24
1       2       67
...
1       1000    56
2       1       59
2       2       46
...
2       1000    64
3       1       54
...
100     1       451
100     2       153
...
100     1000    21

我想添加一个新列prev_value，该列将为每个对象存储以前的value:

I want to add a new column prev_value that will store previous value for each object:

object  period  value  prev_value
1       1       24     nan
1       2       67     24
...
1       99      445    1243
1       1000    56     445
2       1       59     nan
2       2       46     59
...
2       1000    64     784
3       1       54     nan
...
100     1       451    nan
100     2       153    451
...
100     1000    21     1121

我可以以某种方式使用.shift()和.groupby()吗?

Can I use .shift() and .groupby() somehow to do that?

推荐答案

是的，只需:

df['prev_value'] = df.groupby('object')['value'].shift()

对于此示例数据框:

print(df)

     object  period  value
0       1       1     24
1       1       2     67
2       1       4     89
3       2       4      5
4       2      23     23

结果将是:

     object  period  value  prev_value
0       1       1     24         NaN
1       1       2     67        24.0
2       1       4     89        67.0
3       2       4      5         NaN
4       2      23     23         5.0

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