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 m

Answer 1

There are two ways to do this very simply, one without using anything except basic pandas syntax:

df[['x','y']].groupby('x').agg(pd.DataFrame.sample)

This takes 14.4ms with 50k row dataset.

The other, slightly faster method, involves numpy.

df[['x','y']].groupby('x').agg(np.random.choice)

This takes 10.9ms with (the same) 50k row dataset.

Generally speaking, when using pandas, it's preferable to stick with its native syntax. Especially for beginners.