pandas datafram count of each unique value in a column of sentences grouped by code example

Example 1: pandas count the number of unique values in a column

df['hID'].nunique()
5

Example 2: pandas count unique values in column

df.nunique()

Example 3: pandas groupby count unique rows

ID, domain
123, 'vk.com'
123, 'vk.com'
123, 'twitter.com'
456, 'vk.com'
456, 'facebook.com'
456, 'vk.com'
456, 'google.com'
789, 'twitter.com'
789, 'vk.com'