Grouping rows in a list in pandas (python) groupby

Question

I have a DataFrame:

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

I want to group the first element and get the second element as list rows, is it possible?

Answer 1

Yes, this possible by using groupby function to group on the column of your choice and then apply the list to every group: 

df.groupby('a')['b'].apply(list)  

The output you will get as given-below.

a 
A [1, 2] 
B [5, 5, 4] 
C [6]