Re: [Rd] Strange behaviour of the [[ operator (PR#9263)

From: <hpages_at_fhcrc.org>
Date: Sat 30 Sep 2006 - 16:37:15 GMT

Hi Duncan,

This is even more confusing with a matrix:

    > x <- matrix(5:-6, 3)
    > x

         [,1] [,2] [,3] [,4]

    [1,]    5    2   -1   -4
    [2,]    4    1   -2   -5
    [3,]    3    0   -3   -6

    > x[invisible(2),3]
    [1] -2
    > x[2,invisible(3)]
    > .Last.value
    [1] -2

Thanks,
H.

Quoting murdoch@stats.uwo.ca:

> On 9/29/2006 9:06 PM, Herve Pages wrote:
> > Hi,
> >
> > This looks like a bug:
> >
> > > a <- list(b=5)
> > > a[['b']]
> > [1] 5
> > > a[[t<-'b']]
> >
> > Nothing gets printed!
> >
> > I need to use parenthesis to see the expected result:
> >
> > > a[[(t<-'b')]]
> > [1] 5
>
> Yes, I agree it looks like a bug, and it's still there in R-devel. The
> problem is that the assignment sets the R_Visible flag to false, and the
> indexing never sets it to true. The same problem happens with a[t <-
> 'b'], whether a is a list or not:
>
> > a <- c(b=5, c=6, d=7)
> > a[t <- 'b']
> > .Last.value
> b
> 5
>
> Duncan Murdoch
>
> ______________________________________________
> R-devel@r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel
>



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