Thanks for the clarification, Luke. That is really counter-intuitive behavior. I 100% agree with you that the "for" documentation should state that assumption explicitly.
I would also like to suggest changing the "for" implementation to issue a warning if the "seq" argument is a vector of a non-primitive type. That would have saved me a few hours of debugging in the last few days, so I imagine it must be relevant for more people as well. -- Alexandre Sieira CISA, CISSP, ISO 27001 Lead Auditor "The truth is rarely pure and never simple." Oscar Wilde, The Importance of Being Earnest, 1895, Act I Sent with Sparrow (http://www.sparrowmailapp.com/?sig) On Saturday, 9 de March de 2013 at 13:10, luke-tier...@uiowa.edu wrote: > R's for loop is only designed to iterato over primitive types. The > help file says of the seq argument: > > seq: An expression evaluating to a vector (including a list and an > expression) or to a pairlist or ¡NULL¢. A factor value will > be coerced to a character vector. > > [This could be more emphatic by stating that any class attributes are > igonred or something of that nature.] > > Having for() do anything else would require designing an iteration > protocol -- probably would be nice in principle but not easy to do. > > Best, > > luke > > On Sat, 9 Mar 2013, Peter Ehlers wrote: > > > On 2013-03-09 11:14, R. Michael Weylandt wrote: > > > On Sat, Mar 9, 2013 at 6:50 PM, David Winsemius <dwinsem...@comcast.net > > > (mailto:dwinsem...@comcast.net)> > > > wrote: > > > > I was unable to find the reason for the original coercion in the > > > > help("for") page or the R > > > > Language Definition entry regarding for-loops. On the hunch that > > > > coercion > > > > via as.vector > > > > might be occurring, > > > > > > > > > > > > Behaviorally, it seems to, but the code for do_for in eval.c has > > > factors special-cased to call > > > asCharacterFactor so that might not be a robust detail to rely on. The > > > relevant behavior seems instead to be that there's a > > > switch on val_type which creates the loop index but doesn't copy all > > > attributes (like class) > > > > > > Note that this means a user's as.vector wouldn't be called here: > > > > > > as.vector.flub <- function(x, ...) letters[x] > > > > > > foo <- 1:5 > > > class(foo) <- "flub" > > > > > > as.vector(foo) > > > > > > for(j in foo) {print(j); print(class(j))} > > > > > > as.vector.grub <- function(x, ...) match(x, letters) > > > > > > bar <- letters[1:5] > > > class(bar) <- "grub" > > > > > > as.vector(bar) > > > > > > for(j in bar) {print(j); print(class(j))} > > > > > > Cheers, > > > Michael > > > > > > > > I think that Michael is right - the problem is with val_type > > in the do_for code. > > > > Here's a simplified version of Alexandre's example: > > > > d <- as.Date("2013-03-10") > > for(i in seq_along(d)) print(i) > > #[1] 1 > > > > for(i in d) print(i) > > #[1] 15774 > > where we might have expected to see "2013-03-10". > > > > The essential line in the do_for code seems to me to be: > > > > val_type = TYPEOF(val); > > > > ?typeof tells us that R does not have a 'date' type, so: > > > > typeof(d) > > #[1] "double" > > > > And the for-loop results follow. > > > > Peter Ehlers > > > > ______________________________________________ > > R-help@r-project.org (mailto: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. > > > > -- > Luke Tierney > Chair, Statistics and Actuarial Science > Ralph E. Wareham Professor of Mathematical Sciences > University of Iowa Phone: 319-335-3386 > Department of Statistics and Fax: 319-335-3017 > Actuarial Science > 241 Schaeffer Hall email: luke-tier...@uiowa.edu > (mailto:luke-tier...@uiowa.edu) > Iowa City, IA 52242 WWW: http://www.stat.uiowa.edu ______________________________________________ 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.
