python - 升序/重置多索引 Pandas 的整数值

Question

我有一个数据框:

import pandas as pd

tuples = [('a', 1990),('a', 1994),('a',1996),('b',1992),('b',1997),('c',2001)]
index = pd.MultiIndex.from_tuples(tuples, names = ['Type', 'Year'])
vals = ['This','That','SomeName','This','SomeOtherName','SomeThirdName']
df = pd.DataFrame(vals, index=index, columns=['Whatev'])


df
Out[3]: 
                  Whatev
Type Year               
a    1990           This
     1994           That
     1996       SomeName
b    1992           This
     1997  SomeOtherName
c    2001  SomeThirdName

我想添加一列与“年份”相对应的升序整数，该列会针对每个“类型”重置，如下所示:

                  Whatev  IndexInt
Type Year                         
a    1990           This         1
     1994           That         2
     1996       SomeName         3
b    1992           This         1
     1997  SomeOtherName         2
c    2001  SomeThirdName         1

这是我当前的方法:

grouped = df.groupby(level=0)
unique_loc = []
for name, group in grouped:
    unique_loc += range(1,len(group)+1)
joined['IndexInt'] = unique_loc

但这对我来说似乎丑陋且令人费解，我想它在我正在使用的约 5000 万行数据帧上可能会变慢。有没有更简单的方法？

Answer 1

您可以使用groupby(level=0) + cumcount() :

In [7]: df['IndexInt'] = df.groupby(level=0).cumcount()+1

In [8]: df
Out[8]:
                  Whatev  IndexInt
Type Year
a    1990           This         1
     1994           That         2
     1996       SomeName         3
b    1992           This         1
     1997  SomeOtherName         2
c    2001  SomeThirdName         1