[R] unary "-" on logicals
Robert Gentleman
rgentlem at jimmy.harvard.edu
Thu Oct 11 23:53:34 CEST 2001
On Thu, Oct 11, 2001 at 03:38:02PM -0600, HEUMANN,JOHN (A-Loveland,ex1) wrote:
> "An Introduction to R" says that arithmetic operators
> coerce logical vectors to numeric vectors. This doesn't
> seem to be true for unary "-" however:
>
> > x <- 1:10
> > p1 <- (x > 5)
> > p2 <- (-p1)
> > is.logical(p2)
> [1] TRUE
> > is.numeric(p2)
> [1] FALSE
>
> Since "==" always does binary comparison, this can lead to
> some bizarre behavior:
>
> > p1
> [1] FALSE FALSE FALSE FALSE FALSE TRUE TRUE TRUE TRUE TRUE
> > p2
> [1] FALSE FALSE FALSE FALSE FALSE TRUE TRUE TRUE TRUE TRUE
> > (p1 == p2)
> [1] TRUE TRUE TRUE TRUE TRUE FALSE FALSE FALSE FALSE FALSE
> > ((!p1) == (!p2))
> [1] TRUE TRUE TRUE TRUE TRUE TRUE TRUE TRUE TRUE TRUE
If you try
> as.numeric(p1)
[1] 0 0 0 0 0 1 1 1 1 1
> as.numeric(p2)
[1] 0 0 0 0 0 -1 -1 -1 -1 -1
So there is a coercion and a bug,
somehow p2 is not forgetting to be a logical....
>
> Considering that p1 and p2 are both logicals, the last two
> results seem to defy Boolean logic.
>
> Is the fact that -p1 remains a logical instead of a numeric
> intentional or a bug?
>
> Regards,
> -jh-
>
> =========================================
> John M. Heumann, Agilent Technologies
> 815 14th St. S.W., Loveland, CO 80537 USA
> Email: john_heumann at agilent.com
> Phone: 970 679-3761 FAX: 970 679-5399
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