st: generating sums

[Rich Prisinzano <prisinz@eco.utexas.edu>]

I have a data that looks like this:

_obs_  _x_ _y_
 1	1   0
 2	1   0
 3	0   1
 4      0   1
 5	1   0
 6      0   1
 7	0   1

I want to generate a 'streak' variable that will make the data look like
this:

_obs_  _x_ _y_ _z_ _z2_
 1	1   0	1   0
 2	1   0   2   0
 3	0   1   0   1
 4      0   1   0   2
 5	1   0   1   0
 6      0   1   0   1
 7	0   1   0   2

Does anyone have a suggestion? 

Thanks

Rich


-------------------
Richard Prisinzano
Graduate Student
Department of Economics
University of Texas
prisinz@eco.utexas.edu
http://www.eco.utexas.edu/graduate/Prisinzano/

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