[Rd] Re: [R] Several R vs S-Plus issues

[Thomas Lumley]

On Thu, 4 Oct 2001, Kurt Hornik wrote:

> >>>>> David Brahm writes:
> >    - LETTERS[c(NA,2)] in S is c("","B"), but in R is c("NA","B")
>
> I think we do not want to change this.
>
> Splus has
>
> > (1:2)[c(NA,2)]
> [1] NA  2
> > is.na((1:2)[c(NA,2)])
> [1] T F
> > is.na(c(TRUE, FALSE)[c(NA,2)])
> [1] T F
>

I think we do want to change this (as we discussed quite recently) but by
adding a genuine character NA.  The problem is not that LETTERS[c(NA,2)]
returns a missing value, it's that it isn't missing enough. We need a
"NaS" (Not a String) value that can't be confused with Nabisco, but also
can't be confused with an empty string.

	-thomas

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