Re: st: RE: Manipulating dataset in stata

[Cesare Fracassi <cesare.fracassi.2009@anderson.ucla.edu>]

Thank you Nick and Sergiy. It works perfectly.

Nick Cox wrote:
> Assuming that your identifiers run 1 up, then here is one way: 
> local N = _N 
> expand `N' 
> bysort ID : gen ID2 = _n 
> gen DeltaN = . 
> qui forval i = 1/`N' { 
> 	su N if ID == `i', meanonly 
> 	replace DeltaN = N - r(mean) if ID2 == `i' 
> } 
> If your identifiers do not run 1 up, use -egen, group()- to get new
> identifiers that do. 
> Also note 
> FAQ     . . . . . . . . . . . . . . . Expanding datasets to all possible
> pairs
>          2/03    How do I produce a dataset based on all possible
>                 pairs of identifiers within each group?
>                 http://www.stata.com/support/faqs/data/pairs.html
>
> Nick 
> n.j.cox@durham.ac.uk 
> Cesare Fracassi
>
> I have a db that looks like this:
>
> ID   N
> 1      1
> 2      0
> 3      4
> 4      2
> 5      2
> 6      0
> .........
> 10     1
>
>
> (the actual db is much larger than that)
>
> I would like to create a new dataset that contains the nxn possible 
> combinations of observations and takes the differences between the Ns:
>
> ID1   ID2   DeltaN
> 1         1          0 
> 1        2          1
> 1        3         -3
> 1        4         -1
> ........................
> 1      10         0
> 2         1         -1
> 2         2         0
> 2          3         -4
> .......
>
> and so on for the nxn possible combinations...
>
> any idea how to code that in stata?
>
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