find number of non unique rows when doing a groupby in pandas code example

Example 1: pandas groupby count unique rows

df = df.groupby(by='domain', as_index=False).agg({'ID': pd.Series.nunique})
print(df)
    domain  ID
0       fb   1
1      ggl   1
2  twitter   2
3       vk   3

Example 2: dataframe number of unique rows

1
# get the unique values (rows) by retaining last row
2
df.drop_duplicates(keep='last')