[R] selecting rows for inclusion in lm

[Michael Dewey]

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 <jsorkin at grecc.umaryland.edu> 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)
>>jsorkin at grecc.umaryland.edu
>>
>>Confidentiality Statement:
>>This email message, including any attachments, is for the so...{{dropped}}
>>
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>
>
>--
>=================================
>David Barron
>Said Business School
>University of Oxford
>Park End Street
>Oxford OX1 1HP
>
>

Michael Dewey
http://www.aghmed.fsnet.co.uk