st: Number cases into groups based on a shared value

[Mike Lacy <Michael.Lacy@colostate.edu>]

I'm wanting to learn about a "do it yourself" way to do what is 
accomplished by the -group- function in the -egen- command in the following:

set obs 100
gen SomeNum = 10 + int(7 * uniform())
* Attach a sequential group number to all the
* cases with the same value for "SomeNum"
egen GroupNum = group(SomeNum)


This works fine at accomplishing the task.  My interest in the DIY approach 
is that the kind of algorithm I am accustomed  to using for this task does 
not fit with the inner nature <grin> of Stata.  I'm accustomed (in SPSS or 
lower level languages) something like:

sort SomeNum
gen MyGroup = 1 if _n ==1
gen Same = (Somenum = Somenum[_n-1])
gen MyGroup = MyGroup[_n-1] if Same
gen MyGroup = 1+ MyGroup[_n-1] if ! Same

This doesn't fit with how Stat does -if-, as near as I
understand. So, what would the Stata DIY approach to this kind of algorithm 
be?  All I could come up with was to put SomeNum into a matrix so that I 
could loop through it, but that hardly seems like a desirable way to do things.

Thanks,


=-=-=-=-=-=-=-=-=-=-=-=-=
Mike Lacy
Fort Collins CO USA
(970) 491-6721 office





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