[R] sub() of matrix returns a vector and not a matrix

[ripley@stats.ox.ac.uk]

On Tue, 7 May 2002, Martin Maechler wrote:

> >>>>> "Wolfram" == "Wolfram Fischer <- Z/I/M" <wolfram at fischer-zim.ch>> writes:
>
>     Wolfram> Is there a simple possibility to become directly a
>     Wolfram> matrix from a call of sub() on a matrix?
>
> This can be considered as a feature proposal which I would
> second:
>
> sub() and gsub() could be enhanced such as to keep attributes(.)
> of their x argument.
>
> The `dim' attribute which makes a vector into a matrix is just
> one kind of attributes.
>
> Opinions?

Care is needed, as always with attributes (which also include "class", for
example).  As here there is no coercion going on (e.g. data.frame to
matrix or v.v.) preserving dim and dimnames attributes is probably safe,
but class may not be.

>
>
>     >> a <- matrix( letters[1:6], 2, 3 )
>     >> b <- sub( '(.)', '-\\1-', a )
>     Wolfram> 	# I had expected b to be a matrix # but b is a  vector
>     >> print( b )
>     Wolfram> [1] "-a-" "-b-" "-c-" "-d-" "-e-" "-f-"
>
>     >> dim(b) <- dim(a)
>     >> print( b )
>     Wolfram> # b is now a matrix again
>     ....
>
> Martin Maechler <maechler at stat.math.ethz.ch>	http://stat.ethz.ch/~maechler/
> Seminar fuer Statistik, ETH-Zentrum  LEO C16	Leonhardstr. 27
> ETH (Federal Inst. Technology)	8092 Zurich	SWITZERLAND
> phone: x-41-1-632-3408		fax: ...-1228			<><
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-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
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