Pandas - 不同值的滚动累积计数

Question

I have a df like so:

df = pd.DataFrame({
         'date': ['01/01/2020', '01/01/2020', '01/01/2020', '02/01/2020', '02/01/2020', '03/01/2020', '03/01/2020'],
         'id': [101, 102, 103, 101, 104, 105, 106]
})

Output:

         date   id
0  01/01/2020  101
1  01/01/2020  102
2  01/01/2020  103
3  02/01/2020  101
4  02/01/2020  104
5  03/01/2020  105
6  03/01/2020  106

I require a cumulative count of the distinct values like so:

        date   id
0  01/01/2020  3
1  02/01/2020  4
2  03/01/2020  6

I have tried things like df.groupby(['date']).nunique() but obviously that's not right as it gives the unique count for each date, it doesn't have a rolling unique count as I require.

Answer 1

I believe is necesary first remove duplicates per id by DataFrame.drop_duplicates , then get counts per date s by GroupBy.size and add cumulative sum by Series.cumsum :

df = df.drop_duplicates('id').groupby('date').size().cumsum().reset_index(name='id')
print (df)
         date  id
0  01/01/2020   3
1  02/01/2020   4
2  03/01/2020   6

Answer 2

or we can use DataFrame.duplicated :

(~df.duplicated('id')).groupby(df['date']).sum().cumsum().rename('id').reset_index()

         date   id
0  01/01/2020  3.0
1  02/01/2020  4.0
2  03/01/2020  6.0