python - How to count distinct values in a column of a pandas group by object?

Question

I have a pandas data frame and group it by two columns (for example col1 and col2). For fixed values of col1 and col2 (i.e. for a group) I can have several different values in the col3. I would like to count the number of distinct values from the third columns.

For example, If I have this as my input:

1  1  1
1  1  1
1  1  2
1  2  3
1  2  3
1  2  3
2  1  1
2  1  2
2  1  3
2  2  3
2  2  3
2  2  3

I would like to have this table (data frame) as the output:

1  1  2
1  2  1
2  1  3
2  2  1

Answer 1

df.groupby(['col1','col2'])['col3'].nunique().reset_index()