Missing data replacement

Hello,

I would like to know if it is possible to replace missing data of multiple variables for the value of a preexistent data of one variable. Here it is an example to illustrate what I want to do.

Person_number ---- Weight -------- Height

1 -------------------------- 67 -------------- 1,78
2 -------------------------- . -------------- .
3 -------------------------- . -------------- 1,86

In this example, I would like to replace the missing data with the "Person_number" value correspondent to it. In this case "Weight" of the "Person_number"=2 would be 2. However I want to do this process for multiple variables at once.

Best regards,
Arthur