pandas 累计数 [英] Pandas cumulative count

问题描述

我有一个像这样的数据框:

I have a data frame like this:

0        04:10  obj1
1        04:10  obj1
2        04:11  obj1
3        04:12  obj2
4        04:12  obj2
5        04:12  obj1
6        04:13  obj2

想要获得所有对象的累积计数，如下所示:

Wanted to get a cumulative count for all the objects like this:

idx      time   object   obj1_count   obj2_count 
0        04:10  obj1        1             0
1        04:10  obj1        2             0
2        04:11  obj1        3             0
3        04:12  obj2        3             1
4        04:12  obj2        3             2
5        04:12  obj1        4             2
6        04:13  obj2        4             3

尝试使用cumsum，但不确定这是正确的方法.有什么建议吗?

Tried playing with cumsum but not sure that is the right way. Any suggestions?

推荐答案

此操作有一个特殊功能:

There is a special function for such operation: cumcount

>>> df = pd.DataFrame([['a'], ['a'], ['a'], ['b'], ['b'], ['a']], columns=['A'])
>>> df
   A
0  a
1  a
2  a
3  b
4  b
5  a
>>> df.groupby('A').cumcount()
0    0
1    1
2    2
3    0
4    1
5    3
dtype: int64
>>> df.groupby('A').cumcount(ascending=False)
0    3
1    2
2    1
3    1
4    0
5    0
 dtype: int64

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