Subset dataframe and groupby pandas

Question

everyone, I have a data frame such as :

groups  name
1   A
1   B
1   C
1   D
2   E
3   F
3   G
4   H
5   I

and from that I would like to only keep in the data frame the values that are alone in a group:

groups  name
2   E
4   H
5   I

E,H and I are alone in their respective groups.

I tried:

df[df.groupby(['groups']).count() == 1 ]

But it does not seem to be the solution.

Answer 1

Use duplicated :

df[~df.groups.duplicated(keep=False)]

   groups name
4       2    E
7       4    H
8       5    I

Or, drop_duplicates .

df.drop_duplicates('groups', keep=False)

   groups name
4       2    E
7       4    H
8       5    I

Answer 2

将GroupBy.transform用于具有与原始DataFrame相同大小的DataFrame ：

df[df.groupby(['groups'])['name'].transform('size') == 1 ]