Here's an example. dfr <- data.frame(A1=1:10,A2=21:30,B1=31:40,B2=41:50) vars <- colnames(dfr) for (v in vars[grep("B",vars)]) print(mean(dfr[,v]))
> -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf Of Farrel > Buchinsky > Sent: Wednesday, May 03, 2006 10:46 AM > To: r-help@stat.math.ethz.ch > Subject: [R] Listing Variables > > How does one create a vector whose contents is the list of > variables in a > dataframe pertaining to a particular pattern? > This is so simple but I cannot find a straightforward answer. > I want to be able to pass the contents of that list to a "for" loop. > > So let us assume that one has a dataframe whose name is Data. > And let us > assume one had the height of a group of people measured at > various ages. > > It could be made up of vectors Data$PersonalID, Data$FirstName, > Data$LastName, Data$Height.1, Data$Height.5, Data$Height.9, > Data$Height.10,Data$Height.12,Data$Height.20....many many > more variables. > > How would one create a vector of all the Height variable names. > > The simple workaround is to not bother creating the vector > "Data$Height.1" > "Data$Height.5" "Data$Height.9" "Data$Height.10" > "Data$Height.12""Data$Height.20"...but rather just to use the sapply > function. However with some functions the sapply will not > work and it is > necessary to supply each variable name to a function (see thread at > Repeating tdt function on thousands of variables) > > > This is such a core capability. I would like to see it in the > R-Wiki but > could not find it there. > > -- > Farrel Buchinsky, MD > Pediatric Otolaryngologist > Allegheny General Hospital > Pittsburgh, PA > > ______________________________________________ > 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 > ______________________________________________ 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