How to get unique values from multiple columns in a pandas groupby

One more alternative is to use GroupBy.agg with set

df.groupby('c').agg(set)

       l1      l2
c                
1  {a, b}  {d, b}
2  {c, b}  {e, f}

You can do it with apply:

import numpy as np
g = df.groupby('c')['l1','l2'].apply(lambda x: list(np.unique(x)))

Alternatively, you can use agg:

g = df.groupby('c')['l1','l2'].agg(['unique'])

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