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RE: st: Defining upper limit of loop


From   "Sarah Edgington" <sedging@ucla.edu>
To   <statalist@hsphsun2.harvard.edu>
Subject   RE: st: Defining upper limit of loop
Date   Wed, 11 Dec 2013 15:03:30 -0800

Nabin,
It looks like you want Stata to do a different thing depending on the value
of Z for a given observation.  For a given observation, however, you don't
appear to want to do multiple things.

For your simple example you could do this without a loop
gen sum=X+X[_n+1] if Z==1
replace sum=X+X[_n+2] if Z==2
replace sum=X+X[_n+3] if Z==3
replace sum=X+X[_n+4] if Z==4

Of course a loop for something that repeats like this helps prevent typos
and is going to be helpful if you have a lot of values of Z to deal with.

To make it a loop you could do something like:
gen sum=0
sum Z
forv i=1/`r(max)' {
	replace sum =X+X[_n+`i'] if Z==`i'
}

I suspect your actual task is probably more complicated than your example,
in which case this may or may not get you where you're going.  

In general, though, when working with loops I often find it's illuminating
for me to write out exactly what I want to happen for the first couple
iterations of the loop.  If I can get the results I want for those first few
iterations, that often helps make it very clear what the final loop needs to
look like.

-S


-----Original Message-----
From: owner-statalist@hsphsun2.harvard.edu
[mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Thomas, Anthony
Sent: Wednesday, December 11, 2013 2:44 PM
To: statalist@hsphsun2.harvard.edu
Subject: Re: st: Defining upper limit of loop

Yes, a forval loop will work for that. Nick's explanation describes how very
well. I had thought you wanted to actually reference a variable's name (i.e.
a string). Just be aware that the macro `Z'
needs to evaluate to numeric not string. Sorry for the confusion.

Anthony

On Wed, Dec 11, 2013 at 5:30 PM, Nabin Kafle <nkafle89@gmail.com> wrote:
> I want to loop a cycle number of times indicated by a number in a variable
name.
> For example:
> X Y Z
> 1 2 1
> 2 3 4
> 3 2 2
> 3 2 2
> 4 2 2
> . . . .
>
> gen sum=X
> forvalues i=1/"Z" {
> replace sum=X+X[_n+`i']
> }
>
> What would be other way to do such if it is not possible by -forvalues-
command.
>
> On Wed, Dec 11, 2013 at 4:18 PM, Thomas, Anthony 
> <anthony_h_thomas@brown.edu> wrote:
>> Stata probably will not let you do that. Variable names cannot be a 
>> number, and "forval" type loops expect a numeric range (i.e. 
>> "variable name" would have to be a number). If you want to use 
>> variables in a loop, consider using:
>>
>> foreach i of varlist "varlist"{
>>
>>      commands
>>
>> }
>>
>> Anthony
>>
>> On Wed, Dec 11, 2013 at 5:08 PM, Nabin Kafle <nkafle89@gmail.com> wrote:
>>> Is there a way that I can use the forvalues command in stata in a 
>>> way that I upper value of the loop can be defined from the varibale
list.
>>>
>>> forvalues i = 1/"var name" {
>>> code for loop
>>> *
>>> *   For searches and help try:
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>>> *   http://www.ats.ucla.edu/stat/stata/
>> *
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>
>
>
> --
> Nabin Kafle
> *
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