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. ______________________________________________ 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.
