[R] filtering out data

Kate Rohrbaugh krohrbaugh at ipaglobal.com
Fri Aug 22 16:47:06 CEST 2008

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 Rohrbaugh
Independent Project Analysis, Inc.
44426 Atwater Drive
Ashburn, VA  20147
office - 703.726.5465
fax - 703.729.8301
email - krohrbaugh at ipaglobal.com
website - www.ipaglobal.com

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