如何生成相关变量:由income生成aver_income,其中“0”、“.”均不参与计算。谢谢!
| id | year | income |
101 | 2003 | . |
101 | 2004 | 0 |
101 | 2005 | 3000 |
101 | 2006 | 5000 |
102 | 2005 | 2000 |
102 | 2006 | 4000 |
103 | 2003 | 1500 |
103 | 2004 | . |
103 | 2005 | 2500 |
| id | year | income | aver_income |
101 | 2003 | . | 4000 |
101 | 2004 | 0 | 4000 |
101 | 2005 | 3000 | 4000 |
101 | 2006 | 5000 | 4000 |
102 | 2005 | 2000 | 3000 |
102 | 2006 | 4000 | 3000 |
103 | 2003 | 1500 | 2000 |
103 | 2004 | . | 2000 |
103 | 2005 | 2500 | 2000 |