Hi again Julia, Here are two more options: DF<-read.table(textConnection(" x1 x2 x3 1 2 3 4 5 6 7 8 9"),header=TRUE) closeAllConnections()
# Option 1 -- sent before DF$x1+DF$x2 # Option 2 apply(DF,1,function(x) x[1]+x[2]) # Option 3 rowSums(DF[,c(1,2)]) HTH, Jorge On Tue, Jan 20, 2009 at 2:49 PM, Jorge Ivan Velez <jorgeivanve...@gmail.com>wrote: > > Dear Julia, > Try this: > > DF<-read.table(textConnection(" > x1 x2 x3 > 1 2 3 > 4 5 6 > 7 8 9"),header=TRUE) > closeAllConnections() > > DF$x4<-DF$x1+DF$x2 > DF > > > HTH, > > Jorge > > > > On Tue, Jan 20, 2009 at 2:12 PM, Julia Zhou <ms.juliaz...@gmail.com>wrote: > >> Hi, >> >> I would like to operate on certain columns in a dataframe, but not >> others. My data looks like this: >> >> x1 x2 x3 >> 1 2 3 >> 4 5 6 >> 7 8 9 >> >> I want to create a new column named x4 that is the sum of x1 and x2, >> but NOT x3. I looked at colSums and apply, but those functions seem to >> use all the columns in a dataframe. How do I only use select columns? >> >> If it helps, in Stata this would be gen x4 = x1 + x2. >> >> Thanks! >> >> ______________________________________________ >> R-help@r-project.org 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. >> > > [[alternative HTML version deleted]] ______________________________________________ R-help@r-project.org 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.