This advice works best when you use the lapply function to load your data frames to begin with. That way your like-structured data frames are grouped into one list that you can loop through without complicated use of get and assign.
dtadir <- "mydatadir" fnames <- list.files( dtadir ) dtalist <- lapply( fnames, function( fn ) { read.csv( file.path( dtadir, fn ) ) } for ( idx in seq_along( dtalist ) ) { dtalist[[ idx]]$result <- dtalist[[ idx ]][ , 3 ] + dtalist[[ idx ]][ , 4 ] } --------------------------------------------------------------------------- Jeff Newmiller The ..... ..... Go Live... DCN:<jdnew...@dcn.davis.ca.us> Basics: ##.#. ##.#. Live Go... Live: OO#.. Dead: OO#.. Playing Research Engineer (Solar/Batteries O.O#. #.O#. with /Software/Embedded Controllers) .OO#. .OO#. rocks...1k --------------------------------------------------------------------------- Sent from my phone. Please excuse my brevity. On October 15, 2014 8:59:01 PM PDT, Vikash Kumar <vikash.kr....@gmail.com> wrote: >Hi Stephen, > >Try out lapply(). It would help you loop through all data frames and >sum. > >Regards, >Vikash > >On Thu, Oct 16, 2014 at 1:58 AM, Stephen HK Wong <hon...@stanford.edu> >wrote: > >> Dear All, >> >> I have many 50 objects they are all dataframes. Each dataframe has >many >> rows and four column. I simply want to do an addition of 3rd and 4th >column >> and save the result into 5th column. Since there are many dataframes, >I >> don't want to do it one by one, is there a way to loop through all >objects >> and perform the similar action ? >> >> One way I can think of is like this: >> >> for (i in 1:50){ >> get(ls()[i])[,3]+get(ls()[i][,4] >> } >> >> But I don't know how to save the addition result back to 5th column >of >> each dataframe. >> >> >> Many Thanks! >> >> >> >> Stephen HK Wong >> >> ______________________________________________ >> 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. ______________________________________________ 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.