st: Re: Number cases into groups based on a shared value

["Michael Blasnik" <michael.blasnik@verizon.net>]

You can do this in Stata with:

sort SomeNum
gen MyGroup=sum(SomeNum!=SomeNum[_n-1])


Michael Blasnik
michael.blasnik@verizon.net

----- Original Message ----- 
From: "Mike Lacy" <Michael.Lacy@colostate.edu>
To: <statalist@hsphsun2.harvard.edu>
Sent: Monday, March 14, 2005 1:05 PM
Subject: st: Number cases into groups based on a shared value



> 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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