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Re: st: combining two variables


From   "Sergiy Radyakin" <Radyakin@aoek.uni-hannover.de>
To   <statalist@hsphsun2.harvard.edu>
Subject   Re: st: combining two variables
Date   Wed, 7 Mar 2007 18:40:05 +0100


Why would one need "if missing(var1, var2)" ?

gen newvar=max(var1,var2)

produces the same result, unless:

Ambiguity exists, since Paswel Phiri Marenya wanted to "combine the variables in such a way that the data from one variable can replace the missing values from the other". It is as above if the situation of both non-missings is impossible (say, by way the variables are created). If, however, it is possible, then NGC's solution will yield new missings, which contradicts "data ... replace the missings". So because of the way the question is formulated, and because it's not known if both variables may have non-missings, you may wish to consider this code:

gen newvar=var1
replace newvar=var2 if var1==.


Regards, Sergiy


----- Original Message ----- From: "Nick Cox" <n.j.cox@durham.ac.uk>
To: <statalist@hsphsun2.harvard.edu>
Sent: Wednesday, March 07, 2007 6:14 PM
Subject: RE: st: combining two variables



Some very complicated solutions here!

Consider:

gen newvar = max(var1, var2) if missing(var1, var2)

Logic:

If just one of var1 or var2 is missing,
then -missing()- will return true.

In that case, max(var1, var2) will
return the non-missing value in question.

If both are missing, then you get missing returned,
but that is fair enough.

If neither is missing, missing is returned.

Nick
n.j.cox@durham.ac.uk

Paswel Phiri Marenya

What to me is easier is something like:

gen var3 = var2
then replace var3=var1 in 4/5 and so on...although with a
long data set it
may be tedious perhaps.
regrads
PPm

> Thank you to everyone who answered my last question on
> creating a variable corresponding to the row number.
>
> Now I have a question about combining the data from two
> variables (in the same data set) into one variable. I want to
> combine the variables in such a way that the data from one
> variable can replace the missing values from the other. I have
> created an example of what I am looking for below:
>
>
>            Have:                   Want:
>       var1       var2              newvar
>         .          2                 2
>         .          8                 8
>         .          0                 0
>         7          .                 7
>         3          .                 3
>         .          .                 .
>
> Any thoughts on how to do this?
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