How to group dataframe rows into list in pandas groupby

Question

I have a pandas data frame df like:

a b
A 1
A 2
B 5
B 5
B 4
C 6

I want to group by the first column and get second col

Answer 1

If looking for a unique list while grouping multiple columns this could probably help:

df.groupby('a').agg(lambda x: list(set(x))).reset_index()