pandas count distinct values in a column

1df.groupby('mID').agg(['count', 'size', 'nunique']).stack()
2
3
4             dID  hID  uID
5mID                       
6A   count      5    5    5
7    size       5    5    5
8    nunique    3    5    5
9B   count      2    2    2
10    size       2    2    2
11    nunique    2    2    2
12C   count      1    1    1
13    size       1    1    1
14    nunique    1    1    1

1dataframe.column.nunique()

1df['hID'].nunique()
25

1Series.value_counts(self, normalize=False, sort=True, ascending=False, bins=None, dropna=True)