st: variable that counts double observations..

[Linn Renée Naper <linn.naper@ecgroup.no>]

Hi Statalist

egen var=_n, by(group) will give me a variable counting from 1 til N within each group of the data. 
BUT: how do I tell stata that the observations are double in the sense that I need a variable that repeats each number ones, 
like this: 11 22 33 44.... instead of 1 2 3 4.....
I need this variable in order to collapse the data.

Thanks

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