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# Re: st: How do I create a loop that calculates new variables by performing the simple mathematical function of subtracting one varlist on another varlist?

 From James Sams To statalist@hsphsun2.harvard.edu Subject Re: st: How do I create a loop that calculates new variables by performing the simple mathematical function of subtracting one varlist on another varlist? Date Mon, 09 Jan 2012 00:39:36 -0600

```On Monday 09,  January  2012 02:47:44 you wrote:
> I am trying to subtract one sequential list of variables (e.g., a1 to a73)
> from another sequential list (e.g., b1 to b73) using a loop statement such
> as the "foreach..." I am trying to avoid repeating the same, simple
> function (in this case 73 times).
>
> Specifically, I want a loop that repeats this:
>
> gen h7a001=h7r001-h7t001
> gen h7a002=h7r001-h7t002
> to
> gen h7a073=h7r003-h7t073
>
> Simple question but I am trying to learn Stata so that I can use the power
> of its programming capabilities. This particular challenge eludes me.

My preferred solution is to use display as an extended function

. local i 1
. display "`i'"
1
. local j : display %03.0f `i'
. display "`j'"
001

so at the top of your loop, reassign your loop variable, or perhaps make a new
variable This is more general than the previously posted solution.

--
James Sams
sams.james@gmail.com
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