Why not use the subset option? Something like: lm(diff ~ Age + Race, data=data, subset=data$Meno=="PRE")
should do the trick, and be much easier to read! On 18/01/07, John Sorkin <[EMAIL PROTECTED]> wrote: > I am having trouble selecting rows of a dataframe that will be included > in a regression. I am trying to select those rows for which the variable > Meno equals PRE. I have used the code below: > > difffitPre<-lm(data[,"diff"]~data[,"Age"]+data[,"Race"],data=data[data[,"Meno"]=="PRE",]) > summary(difffitPre) > > The output from the summary indicates that more than 76 rows are > included in the regression: > > Residual standard error: 2.828 on 76 degrees of freedom > > where in fact only 22 rows should be included as can be seen from the > following: > > print(data[length(data[,"Meno"]=="PRE","Meno"])) > [1] 22 > > I would appreciate any help in modifying the data= parameter of the lm > so that I include only those subjects for which Meno=PRE. > > R 2.3.1 > Windows XP > > Thanks, > John > > John Sorkin M.D., Ph.D. > Chief, Biostatistics and Informatics > Baltimore VA Medical Center GRECC, > University of Maryland School of Medicine Claude D. Pepper OAIC, > University of Maryland Clinical Nutrition Research Unit, and > Baltimore VA Center Stroke of Excellence > > University of Maryland School of Medicine > Division of Gerontology > Baltimore VA Medical Center > 10 North Greene Street > GRECC (BT/18/GR) > Baltimore, MD 21201-1524 > > (Phone) 410-605-7119 > (Fax) 410-605-7913 (Please call phone number above prior to faxing) > [EMAIL PROTECTED] > > Confidentiality Statement: > This email message, including any attachments, is for the so...{{dropped}} > > ______________________________________________ > R-help@stat.math.ethz.ch mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code. > -- ================================= David Barron Said Business School University of Oxford Park End Street Oxford OX1 1HP ______________________________________________ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.