stata如何任何两个城市间指标的循环计算

现有数据如下：有4个城市，各3年数据，3个变量，分别为humcaptal wage house
. dataex city year humcaptal wage house

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1. * Example generated by -dataex-. To install: ssc install dataex
   
2. clear
   
3. input float(city year humcaptal wage house)
   
4. 1 2003 4 3 2
   
5. 1 2004 8 5 1
   
6. 1 2005 2 1 1
   
7. 2 2003 3 2 1
   
8. 2 2004 5 4 2
   
9. 2 2005 7 9 8
   
10. 3 2003 2 3 1
    
11. 3 2004 1 2 3
    
12. 3 2005 4 5 6
    
13. 4 2003 1 5 6
    
14. 4 2004 6 5 4
    
15. 4 2005 7 8 9
    
16. end

复制代码

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Listed 12 out of 12 observations
还有个距离矩阵distance如下
      1     2    3
1   0      6    7
2   8     0     5
3  7     5      0
.
想要对每个城市分别生成各个年份的新变量pfl



感谢各位大神解答，不胜感激涕零