Count unique values with pandas per groups

Question

I need to count unique ID values in every domain I have data

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'

I try df.groupby(['domain', 'ID']).count(). But I want to get

domain, count

vk.com   3

twitter.com   2

facebook.com   1

google.com   1

Answer 1

Use df.domain.value_counts():

>>> df.domain.value_counts()

vk.com          5

twitter.com     2

google.com      1

facebook.com    1

Name: domain, dtype: int64

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