You can try for testing with a column of class errors, from the package 'errors'. The attributes depend on the content in the way Hadley pointed out.
Iñaki El lun., 4 nov. 2019 23:19, Rolf Turner <r.tur...@auckland.ac.nz> escribió: > On 5/11/19 10:54 AM, Duncan Murdoch wrote: > > On 04/11/2019 4:40 p.m., Pages, Herve wrote: > >> Hi Rolf, > >> > >> On 11/4/19 12:28, Rolf Turner wrote: > >>> > >>> On 5/11/19 3:41 AM, Hadley Wickham wrote: > >>> > >>>> For what it's worth, I don't think this strategy can work in general, > >>>> because a class might have attributes that depend on its data/contents > >>>> (e.g. > >>>> > https://urldefense.proofpoint.com/v2/url?u=https-3A__vctrs.r-2Dlib.org_articles_s3-2Dvector.html-23cached-2Dsum&d=DwICAg&c=eRAMFD45gAfqt84VtBcfhQ&r=BK7q3XeAvimeWdGbWY_wJYbW0WYiZvSXAJJKaaPhzWA&m=pqLHzHYLUeyQnxA1K_XhSbKJql6r9wK1RXcDG2tuZ6s&s=kPUlNqBPr6j4lPvqkIj8w2Gl5JYGLqJ7ws6wH5tpGcw&e= > >>>> > >>>> ). I > >>>> don't think these are particularly common in practice, but it's > >>>> dangerous to assume that you can restore a class simply by restoring > >>>> its attributes after subsetting. > >>> > >>> > >>> You're probably right that there are lurking perils in general, but I > am > >>> not trying to "restore a class". I simply want to *retain* attributes > >>> of columns in a data frame. > >>> > >>> * I have a data frame X > >>> * I attach attributes to certain of its columns; > >>> attr(X$melvin,"clyde") <- 42 > >>> (I *don't* change the class of X$melvin.) > >>> * I form a subset of X: > >>> Y <- X[1:100,3:10] > >>> * given that "melvin" is amongst columns 3 through 10 of X, > >>> I want Y$melvin to retain the attribute "clyde", i.e. I > >>> want attr(Y$melvin,"clyde") to return 42 > >>> > >>> There is almost surely a better approach than the one that I've chosen > >>> (isn't there always?) but it seems to work, and the perils certainly > are > >>> not immediately apparent to me. > >> > >> Maybe you've solved the problem for the columns that contain your > >> objects but now you've introduced a potential problem for columns that > >> contain objects with attributes whose value depend on content. > >> > >> Hadley it right that restoring the original attributes of a vector (list > >> or atomic) after subsetting is unsafe. > > > > Right, so Rolf should only restore attributes that are ones he added in > > the first place. Unknown attributes should be left alone. > > Fair point. And that gets fiddly. I guess I'm going to have to rethink > my strategy. > > cheers, > > Rolf > > -- > Honorary Research Fellow > Department of Statistics > University of Auckland > Phone: +64-9-373-7599 ext. 88276 > > ______________________________________________ > R-devel@r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-devel > [[alternative HTML version deleted]] ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
