At 08:19 18/01/2007, David Barron wrote: >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!
And indeed the advice in > library(fortunes) > fortune("dog") Firstly, don't call your matrix 'matrix'. Would you call your dog 'dog'? Anyway, it might clash with the function 'matrix'. -- Barry Rowlingson R-help (October 2004) > also helps to make life clearer I find >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 > > Michael Dewey http://www.aghmed.fsnet.co.uk ______________________________________________ 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.