count unique values in a series pandas code example

Example 1: count unique pandas

df['column'].nunique()

Example 2: 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 3: pandas count distinct values in column

#column name ISSDTM
pd.to_datetime(df.ISSDTM, errors='coerce').dt.year

#result
0    2013
1    2013
2    2009
3    2009
Name: ISSDTM, dtype: int64