将GROUP BY结果附加到原始表中

Question

 col = full.groupby('state')[['demVote']].mean()

full是原始表的名称。我如何将这个group by语句的结果作为称为'DEM'的列附加到原始表中？

Answer 1

我认为这可以解决问题，如果不能，请提供具体示例？

full['DEM'] = full.groupby('state').mean()['demVote']

Answer 2

使用transform：

full['DEM'] = full.groupby('state')['demVote'].transform('mean')

例如：

>>> full
   demVote state
0        1    ca
1        2    ca
2        3    ny
3        4    ny

full['DEM'] = full.groupby('state')['demVote'].transform('mean')

>>> full
   demVote state  DEM
0        1    ca  1.5
1        2    ca  1.5
2        3    ny  3.5
3        4    ny  3.5