[Rd] is.na<- problem

[Gabor Grothendieck]

On 10/19/05, Marc Schwartz <MSchwartz at mn.rr.com> wrote:
> On Thu, 2005-10-20 at 01:13 +0100, Ted Harding wrote:
> > On 19-Oct-05 Gabor Grothendieck wrote:
> > > In the following the first element of xx should have
> > > been set to 0 but remains NA.  Any comments?
> > >
> > >> xx <- c(NA,1)
> > >> is.na(xx) <- 0
> > >> xx
> > > [1] NA  1
> > >> R.version.string # Windows XP
> > > [1] "R version 2.2.0, 2005-09-20"
> >
> > I wonder, has it ever worked? I get the same as you on
> >
> > R.version.string #Linux
> > [1] "R version 1.6.2, 2003-01-10"
> >
> > R.version.string #Linux
> > [1] "R version 1.8.0, 2003-10-08"
> >
> > R.version.string #Linux
> > [1] "R version 2.1.0, 2005-04-08"
> >
> > with the exception of
> >
> > R.version.string #Linux
> > [1] "R version 1.2.3, 2001-04-26"
> >
> > which does know about is.na()<- at all.
> >
> >
> > Hmmm
> > Ted.
>
> According to the documentation in ?is.na:
>
>   The generic function is.na<- sets elements to NA.
>
> and in the details section:
>
> Function is.na<- may provide a safer way to set missingness. It behaves
> differently for factors, for example.
>
>
> In reviewing the Green Book on the top of page 143, it shows an example
> in which the RHS of the assignment are the indices into the LHS object
> which are to be set to NA. For example:
>
> > xx <- c(0:5)
>
> > xx
> [1] 0 1 2 3 4 5
>
> > is.na(xx) <- c(3, 4)
>
> > xx
> [1]  0  1 NA NA  4  5
>
>
> Thus, back to Gabor's example, the proper approach would of course be:
>
> > xx <- c(NA,1)
>
> > xx
> [1] NA  1
>
> > xx[is.na(xx)] <- 0
>
> > xx
> [1] 0 1
>
>
> HTH,
>
> Marc Schwartz
>
>
>


Thanks.  I actually had read ?is.na but obviously not closely enough.