st: Extend observations in dataset

["Peter Bilfiger" <peter_bilfiger@web.de>]

I have the following dataset:
 
Number       Year     Other variable of interest
11111        1999      5


Now, I want to extend the observations so that it looks like this:

Number     Year     Other variable of interest
11111      1999     5
11111      2000     .
11111      2001     .
11111      2002     .
11111      1998     .
11111      1997     .
11111      1996     .
      

Basically extend the years by +3 and -3 and just copy the number so that for each year, there is the same number from the initial year. The other variables are not important. They can be missing.

Can anybody help?

Thank you.

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