for in r-devel
Thanks for pointing this out. The commit you cite was reverted a couple days later, because we are still thinking about how it should work. While it appears Date would benefit, weird things happen e.g. with POSIXlt and other data structures in the wild. This is due to inconsistency in the behaviors of length() and [[() methods. One thought is introducing a generic that coerces to something with consistent behavior, e.g. iterable(). We were even thinking that an iterable might be allowed to return NA for length, in which case it would need to support methods like next() and hasNext(). Ideas welcome. Michael On Fri, Mar 18, 2016 at 7:25 AM, Gabor Grothendieck <ggrothendieck at gmail.com
wrote:
Regarding, this news item for r-devel: ?for()? loops are generalized to iterate over any object with ?[[? and ?length()? methods. Thanks to Herv? Pag?s for the idea and the patch. Below dd is an object for which [[ and length work but the result is still numeric rather than Date class in "R Under development (unstable) (2016-03-15 r70334)" as observed in the comments to: http://stackoverflow.com/questions/36074344/why-does-for-convert-date-to-numeric#comment59794873_36074344 Expanding on that: dd <- Sys.Date() + 0:1 dd[[1]] # [[ works ## [1] "2016-03-18" length(dd) # length works ## [1] 2 for(d in dd) str(d) # gives numeric rather than Date class ## num 16878 ## num 16879 -- Statistics & Software Consulting GKX Group, GKX Associates Inc. tel: 1-877-GKX-GROUP email: ggrothendieck at gmail.com
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