如下表:
| company | date | sales |
| 1001 | 200509 | 20 |
| 1001 | 200603 | 30 |
| 1016 | 200603 | 451 |
| 1016 | 200606 | 521 |
| 1016 | 200609 | 358 |
| 1016 | 2006012 | 650 |
增加新的行,至于新增的sales值则设为missing value ‘.’:
| company | date | sales |
| 1001 | 200509 | 20 |
| 1001 | 200510 | . |
| 1001 | 200511 | . |
| 1001 | 200512 | . |
| 1001 | 200601 | . |
| 1001 | 200602 | . |
| 1001 | 200603 | 30 |
| 1016 | 200603 | 451 |
| 1016 | 200604 | . |
| 1016 | 200605 | . |
| 1016 | 200606 | 521 |
| 1016 | 200607 | . |
| 1016 | 200608 | . |
| 1016 | 200609 | 358 |
| 1016 | 200610 | . |
| 1016 | 200611 | . |
| 1016 | 2006012 | 650 |
望指点一二!




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