how to count different values in a column in pandas code example

Example 1: get count of unique values in column pandas

df = df.groupby('domain')['ID'].nunique()

print (df)
domain
'facebook.com'    1
'google.com'      1
'twitter.com'     2
'vk.com'          3
Name: ID, dtype: int64

Example 2: count unique values pandas

df['hID'].nunique()
5