This seems more or less correct to me. 1> sum(df$a==1) [1] 1 1> sum(df$a==2) [1] 1 1> sum(df$aaa==2) [1] 0
There is no df$aaa so the length is 0 which is what I think you are asking. What am I missing? John Kane Kingston ON Canada > -----Original Message----- > From: paulo.bar...@ensp.fiocruz.br > Sent: Sun, 15 Jul 2012 11:30:37 -0300 > To: r-help@r-project.org > Subject: [R] variable (column) in a data frame > > > To the R help list, > > When using a data frame, there is no warning or error message > when I refer to a non-existent variable inside the data frame. > > Example: > > ##---------------------------------------------- > > a <- c(1,2,3) > b <- c(11,22,33) > df <- data.frame(a,b) > df > > ## correct: there is a column in df named 'a' > ## the sum is correctly performed > sum(df$a==2) > > ## incorrect: there is no column in df named 'aaa', > ## but the sum is performed anyway without either warning or error > sum(df$aaa==2) > > ##---------------------------------------------- > > Is there some way to make R issue either a warning or an error > message in such a situation? > > I am using R version 2.15.1 64-bit on Windows 7 Professional. > > Thank you very much. > > Paulo Barata > > --------------------------------------------------------------------- > Paulo Barata > > ENSP - Fundação Oswaldo Cruz > Rua Leopoldo Bulhões 1480 - 8A > 21041-210 Rio de Janeiro - RJ > Brazil > E-mail: paulo.bar...@ensp.fiocruz.br > > ______________________________________________ > 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. ____________________________________________________________ GET FREE SMILEYS FOR YOUR IM & EMAIL - Learn more at http://www.inbox.com/smileys Works with AIM®, MSN® Messenger, Yahoo!® Messenger, ICQ®, Google Talk™ and most webmails ______________________________________________ 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.
