On Thu, 26 Aug 2010, Martin Maechler wrote:
"WD" == William Dunlap <wdun...@tibco.com>
on Wed, 25 Aug 2010 17:31:27 -0700 writes:
WD> Should there be a [[<-.factor() that either throws
WD> an error or acts like [<-.factor() to avoid making
WD> an illegal object of class factor?
Yes, one or the other.
Note that both `[<-` and `[[<-` are "Primitive" and do some
"informal dispatch" in addition to the formal method dispatch,
I don't think so. do_subassign2 does formal method dispatch, albeit
internally, but nothing else (do_assign2_dflt selects only by
typeof()).
so there's no need for an explicit '[[<-.factor' method definition.
For factors, it seems rational and "expectable" that
double bracket behaves as single bracket when *one* element is
assigned.
z[[2:3]] <- c("Two, Three")
however should continue to give an error.
I added a [[<-.factor yesterday. Note that we do have a [<-.factor
which works on the integer codes, and I simply copied its logic.
BTW, you probably meant
z[[2:3]] <- c("Two", "Three")
Martin Maechler, ETH Zurich
>> z <- factor(c("Two","Two","Three"), levels=c("One","Two","Three"))
>> z
WD> [1] Two Two Three
WD> Levels: One Two Three
>> str(z)
WD> Factor w/ 3 levels "One","Two","Three": 2 2 3
>> z[[2]] <- "One"
>> str(z) # the .Data part is now character
WD> Factor w/ 3 levels "One","Two","Three": 2 One 3
>> z
WD> [1] <NA> <NA> <NA>
WD> Levels: One Two Three
>> z[2] <- "One"
WD> Error in class(x) <- cx : adding class "factor" to an invalid object
WD> Bill Dunlap
WD> Spotfire, TIBCO Software
WD> wdunlap tibco.com
WD> ______________________________________________
WD> R-devel@r-project.org mailing list
WD> https://stat.ethz.ch/mailman/listinfo/r-devel
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Brian D. Ripley, rip...@stats.ox.ac.uk
Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/
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