Count of unique value in column pandas [duplicate]

Answer 1

You could use group by to achieve that:

df[['col1']].groupby(['col1']).agg(['count'])

Answer 2

If I understand you correctly, you can use pandas.Series.value_counts.

Example:

import pandas as pd
import numpy as np

s = pd.Series(['Katherine', 'Robert', 'Anne', np.nan, 'Susan', 'other'])

s.value_counts()

Katherine    1
Robert       1
other        1
Anne         1
Susan        1
dtype: int64

The data you provided only has one of each name - so here is an example with multiple 'Katherine' entries:

s = pd.Series(['Katherine','Katherine','Katherine','Katherine', 'Robert', 'Anne', np.nan, 'Susan', 'other'])

s.value_counts()

Katherine    4
Robert       1
other        1
Anne         1
Susan        1
dtype: int64

When applied to your Dataframe you will call this as follows:

df['names'].value_counts()