假设的例子:
| stkcd | year | donation | ydo |
1 | 2003 | 500 | 1300 |
1 | 2003 | 0 | 1300 |
1 | 2003 | 800 | 1300 |
1 | 2004 | 0 | 700 |
1 | 2004 | 700 | 700 |
我用了 bysort stkcd year: gen ydo=sum(donation)
结果得出的是下面的:
| stkcd | year | donation | ydo |
1 | 2003 | 500 | 500 |
1 | 2003 | 0 | 500 |
1 | 2003 | 800 | 1300 |
1 | 2004 | 0 | 0 |
1 | 2004 | 700 | 700 |


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