Martin Maechler wrote:
> > "AndyL" == Liaw, Andy <[EMAIL PROTECTED]>
> > on Tue, 4 Oct 2005 13:51:11 -0400 writes:
>
> AndyL> The `problem' is that sort() does not doing anything special when
> given
> AndyL> a matrix: it only treat it as a vector. After sorting, it copies
> AndyL> attributes of the original input to the output. Since dimnames are
> AndyL> attributes, they get copied as is.
>
> exactly. Thanks Andy.
>
> And I think users would want this (copying of attributes) in
> many cases; in particular for user-created attributes
>
> ?sort really talks about sorting of vectors and factors;
>and it doesn't mention attributes explicitly at all
>{which should probably be improved}.
>
> One could wonder if R should keep the dim & dimnames
> attributes for arrays and matrices.
> S-plus (6.2) simply drops them {returning a bare unnames vector}
> and that seems pretty reasonable to me.
This is as described in the Blue book, p.146, "Throwing Away Attributes".
>
> At least the user would never make the wrong assumptions that
> Greg made about ``matrix sorting''.
>
>
> AndyL> Try:
>
> >> y <- matrix(8:1, 4, 2, dimnames=list(LETTERS[1:4], NULL))
> >> y
> AndyL> [,1] [,2]
> AndyL> A84
> AndyL> B73
> AndyL> C62
> AndyL> D51
> >> sort(y)
> AndyL> [,1] [,2]
> AndyL> A15
> AndyL> B26
> AndyL> C37
> AndyL> D48
>
> AndyL> Notice the row names stay the same. I'd argue that this is the
> correct
> AndyL> behavior.
>
> AndyL> Andy
>
>
> >> From: Greg Finak
> >>
> >> Not sure if this is the correct forum for this,
>
> yes, R-devel is the proper forum.
> {also since this is really a proposal for a change in R ...}
>
> >> but I've found what I
> >> would consider to be a potentially serious bug to the
> >> unsuspecting user.
> >> Given a numeric vector V with class labels in R, the following calls
> >>
> >> 1.
> >> > sort(as.matrix(V))
> >>
> >> and
> >>
> >> 2.
> >> >as.matrix(sort(V))
> >>
> >> produce different ouput. The vector is sorted properly in
> >> both cases,
> >> but only 2. produces the correct labeling of the vector. The call to
> >> 1. produces a vector with incorrect labels (not sorted).
> >>
> >> Code:
> >> >X<-c("A","B","C","D","E","F","G","H")
> >> >Y<-rev(1:8)
> >> >names(Y)<-X
> >> > Y
> >> A B C D E F G H
> >> 8 7 6 5 4 3 2 1
> >> > sort(as.matrix(Y))
> >> [,1]
> >> A1
> >> B2
> >> C3
> >> D4
> >> E5
> >> F6
> >> G7
> >> H8
> >> > as.matrix(sort(Y))
> >> [,1]
> >> H1
> >> G2
> >> F3
> >> E4
> >> D5
> >> C6
> >> B7
> >> A8
> >>
>
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--
David
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