Python: Random selection per group

Question

Say that I have a dataframe that looks like:

Name Group_Id AAA  1 ABC  1 CCC  2 XYZ  2 DEF  3  YYH  3 

How could I randomly select one (or more) row for each Group_Id? Say that I want one random draw per Group_Id, I would get:

Name Group_Id AAA  1 XYZ  2 DEF  3 

Answer 1

size = 2        # sample size replace = True  # with replacement fn = lambda obj: obj.loc[np.random.choice(obj.index, size, replace),:] df.groupby('Group_Id', as_index=False).apply(fn) 

Answer 2

From 0.16.x onwards pd.DataFrame.sample provides a way to return a random sample of items from an axis of object.

In [664]: df.groupby('Group_Id').apply(lambda x: x.sample(1)).reset_index(drop=True) Out[664]:   Name  Group_Id 0  ABC         1 1  XYZ         2 2  DEF         3