I want "an b column value" add to "other b column value" which are same "a" column values
for python ↓↓↓
| Column A | Column B |
|---|---|
| title1 | 15 |
| title2 | 12 |
| title2 | 18 |
| title3 | 8 |
| title3 | 13 |
| title4 | 7 |
I have this dataframe ↑
How can i transform to this one ↓
| Column A | Column B |
|---|---|
| title1 | 15 |
| title2 | 30 |
| title3 | 21 |
| title4 | 7 |
