But it's also a convenience feature. Note that $E returned null because there was an ambiguity. By the time you got to $Ex the column you were referencing was unambiguous and you didn't have to type out the whole thing. Useful if you have very long column names, for example imported from a spreadsheet.
That said, I agree that relying on it can be risky. Also, please use plain-text to post to this list. Your table would have been much easier to read. Pat On Thu, Jul 18, 2019 at 11:56 AM Sarah Goslee <sarah.gos...@gmail.com> wrote: > > Hello Yannick, > > That behavior is documented in the help for subsetting ( ?'$' ): > > Both ‘[[’ and ‘$’ select a single element of the list. The main > difference is that ‘$’ does not allow computed indices, whereas > ‘[[’ does. ‘x$name’ is equivalent to ‘x[["name", exact = > FALSE]]’. Also, the partial matching behavior of ‘[[’ can be > controlled using the ‘exact’ argument. > > You can avoid it by using [[]] instead: > > > swiss[['Ex']] > NULL > > head(swiss[['Examination']]) > [1] 15 6 5 12 17 9 > > That's one of the major reasons using $ is sometimes discouraged. > > Sarah > > On Thu, Jul 18, 2019 at 11:38 AM <yannick.su...@coop.ch> wrote: > > > > Hello all > > I noticed today that you can access dataframe columns by using incomplete > > names. This is a really unexpected behavior which led to some unexpected > > errors and I was wondering whether it's a bug or not and whether it should > > be changed in the future. > > Here's a working example using the preinstalled "swiss" dataset: > > > > > head(swiss) > > Fertility Agriculture Examination Education Catholic > > Courtelary 80.2 17.0 15 12 9.96 > > Delemont 83.1 45.1 6 9 84.84 > > Franches-Mnt 92.5 39.7 5 5 93.40 > > Moutier 85.8 36.5 12 7 33.77 > > Neuveville 76.9 43.5 17 15 5.16 > > Porrentruy 76.1 35.3 9 7 90.57 > > Infant.Mortality > > Courtelary 22.2 > > Delemont 22.2 > > Franches-Mnt 20.2 > > Moutier 20.3 > > Neuveville 20.6 > > Porrentruy 26.6 > > > swiss$E > > NULL > > > swiss$Ex > > [1] 15 6 5 12 17 9 16 14 12 16 14 21 14 19 22 18 17 26 31 19 22 14 22 20 > > 12 > > [26] 14 6 16 25 15 3 7 5 12 7 9 3 13 26 29 22 35 15 25 37 16 22 > > > swiss$Ed > > [1] 12 9 5 7 15 7 7 8 7 13 6 12 7 12 5 2 8 28 20 9 10 3 12 6 > > 1 > > [26] 8 3 10 19 8 2 6 2 6 3 9 3 13 12 11 13 32 7 7 53 29 29 > > > > So in order to access the column "Examination", I can type any substring > > from "Ex" to "Examination" and will always get the column swiss$Examination. > > > > Thanks for reading and Greetings > > Yannick Suter > > > -- > Sarah Goslee (she/her) > http://www.numberwright.com > > ______________________________________________ > R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see > 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 -- To UNSUBSCRIBE and more, see 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.
