如何在pandas中创建新列，该列是基于条件的另一列的总和？

Question

I am trying to get the result column to be the sum of the value column for all rows in the data frame where the country is equal to the country in that row, and the date is on or before the date in that row.

Date        Country ValueResult
01/01/2019  France  10  10
03/01/2019  England 9   9
03/01/2019  Germany 7   7
22/01/2019  Italy   2   2
07/02/2019  Germany 10  17
17/02/2019  England 6   15
25/02/2019  England 5   20
07/03/2019  France  3   13
17/03/2019  England 3   23
27/03/2019  Germany 3   20
15/04/2019  France  6   19
04/05/2019  England 3   26
07/05/2019  Germany 5   25
21/05/2019  Italy   5   7
05/06/2019  Germany 8   33
21/06/2019  England 3   29
24/06/2019  England 7   36
14/07/2019  France  1   20
16/07/2019  England 5   41
30/07/2019  Germany 6   39
18/08/2019  France  6   26
04/09/2019  England 3   44
08/09/2019  Germany 9   48
15/09/2019  Italy   7   14
05/10/2019  Germany 2   50

I have tried the below code but it sums up the entire column

df['result'] = df.loc[(df['Country'] == df['Country']) & (df['Date'] >= df['Date']), 'Value'].sum()

Answer 1

按照日期排序，您可以执行以下操作：

df['Result'] = df.grouby('Coutry').Value.cumsum()