Thank you, thank you everyone!
 
This last worked the best for what I need to do.  The other options were definitely helpful in that they help me understand how R is structured (something I haven't been able to get my head around yet) and gave me good ideas about how to manipulate data, however they generated regressions of data I don't care about (i.e., when "model1"==0).   
 
Regards -- Kate
 
Kate Rohrbaugh
Independent Project Analysis, Inc.
44426 Atwater Drive
Ashburn, VA  20147
 
office - 703.726.5465
fax - 703.729.8301
email - krohrbaugh@ipaglobal.com 
website - www.ipaglobal.com ( http://www.ipaglobal.com/ )


>>> Daniel Folkinshteyn <dfolkins@gmail.com> 8/22/2008 12:08 PM >>>
If I understand correctly the result you are trying to achieve, I think 
what you may be looking for is this:

model1.coeff <- lm(dv ~ iv1 + iv2 + iv3, data = 
merged.dataset[merged.dataset$model1 == 1, ])

This will give you a regression using only the data for which model1 == 1.

on 08/22/2008 11:07 AM jim holtman said the following:
> Exactly what do you want this statement to do:
> 
> if(merged.dataset$model1 == 1) model1.coeff <- lm(dv ~ iv1 + iv2 +
> iv3, data = merged.dataset)
> 
> The result in the "if" is a vector of logical values (assuming that
> merged.dataset is longer than 1); that is the source of the error
> message.  Do you want the regression to be done on every row?  So what
> is the problem you are trying to solve?
> 
> On Fri, Aug 22, 2008 at 10:47 AM, Kate Rohrbaugh
> <krohrbaugh@ipaglobal.com> wrote:
>> Greetings,
>>
>> Apologies for such a simple question, but I have been trying to figure this out for a few days now (I'm quite new to R), have read manuals, list posts, etc., and not finding precisely what I need.  I am accustomed to working in Stata, but I am currently working through the multilevel package right now.  In Stata, I would include the statement "if model1 == 1" at the end of my regression statement, but I can't seem to find the correct syntax for doing the same thing in R.
>>
>> I have successfully converted Stata datasets, merged, aggregated, run lm, etc., but this simple task is evading me entirely.
>>
>> Here's what I have tried (and various iterations):
>>
>> if(merged.dataset$model1 == 1) model1.coeff <- lm(dv ~ iv1 + iv2 + iv3, data = merged.dataset)
>> I get this:
>> Warning message:
>> In if (merged.dataset$model1 == 1) model1.coeff <- lm(dv ~ iv +  :
>>  the condition has length > 1 and only the first element will be used
>> What it seems to do is just run lm on the first opportunities of model1==1, but then doesn't try it again.  I tried sorting so that the model1==1 appear first, but that doesn't seem to be a great solution either.
>>
>> I'll just go back into Stata and create separate new datasets if I have to, but there HAS to be a more elegant way.
>>
>> Thank you for ANY feedback!
>>
>> Kate
>>
>> Kate Rohrbaugh
>> Independent Project Analysis, Inc.
>> 44426 Atwater Drive
>> Ashburn, VA  20147
>>
>> office - 703.726.5465
>> fax - 703.729.8301
>> email - krohrbaugh@ipaglobal.com 
>> website - www.ipaglobal.com 
>>
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