Pandas number rows within group in increasing order
Use groupby/cumcount:
In [25]: df['C'] = df.groupby(['A','B']).cumcount()+1; dfOut[25]: A B C0 A a 11 A a 22 A b 13 B a 14 B a 25 B a 3
Use groupby.rank function.Here the working example.
df = pd.DataFrame({'C1':['a', 'a', 'a', 'b', 'b'], 'C2': [1, 2, 3, 4, 5]})dfC1 C2a 1a 2a 3b 4b 5df["RANK"] = df.groupby("C1")["C2"].rank(method="first", ascending=True)dfC1 C2 RANKa 1 1a 2 2a 3 3b 4 1b 5 2