How to add sequential counter column on groups using Pandas groupby

Question

I feel like there is a better way than this:

import pandas as pd
df = pd.DataFrame(
    [[\'A\', \'X\', 3], [\'A\', \'X\', 5], [\'A\', \'Y\', 7], [\'A\', \'Y         


        

Answer 1

This might be useful

df = df.sort_values(['userID', 'date'])
grp = df.groupby('userID')['ItemID'].aggregate(lambda x: '->'.join(tuple(x))).reset_index()
print(grp)

it will create a sequence like this