Dear Frans and Peter, Yes, the notation df[,'var'] is able to catch a non-existent variable var inside a data frame df. But the notation df$var isn't.
So we have this situation, where two different notations, which (as far as I understand) perform the same action, have different kinds of response. Couldn't this situation be fixed? Isn't it possible to make the df$var notation to issue an error when referring to a non-existent variable inside the data frame? Thank you very much. Paulo Barata --------------------------------------------------------------------- ---------- Original Message ----------- From: "Frans Marcelissen" <frans.marcelis...@digipsy.nl> To: "'Paulo Barata'" <paulo.bar...@ensp.fiocruz.br>, <r-help@r-project.org> Sent: Mon, 16 Jul 2012 14:25:21 +0200 Subject: RE: [R] variable (column) in a data frame > Hoi Pauli, > There is a difference between two ways of accessing columns in a matrex: > > df$aaa > NULL > > df["AAA"] > Error in `[.data.frame`(df, "AAA") : undefined columns selected > So df["AAA"] or df[,"AAA"] gives the error message you expect. > ------------------- > Frans > > -----Oorspronkelijk bericht----- > Van: r-help-boun...@r-project.org [mailto:r-help-boun...@r-project.org] > Namens Paulo Barata > Verzonden: zondag 15 juli 2012 16:31 > Aan: r-help@r-project.org > Onderwerp: [R] variable (column) in a data frame > > To the R help list, > > When using a data frame, there is no warning or error message when I > refer to a non-existent variable inside the data frame. > > Example: > > ##---------------------------------------------- > > a <- c(1,2,3) > b <- c(11,22,33) > df <- data.frame(a,b) > df > > ## correct: there is a column in df named 'a' > ## the sum is correctly performed > sum(df$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. > > -- > This message has been scanned for viruses and > dangerous content by MailScanner, and is > believed to be clean. ------- End of Original Message ------- ______________________________________________ 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.