R help - May 2002 - sub() of matrix returns a vector and not a matrix

Is there a simple possibility
to become directly a matrix
from a call of sub() on a matrix?


--------- START OF LOGFILE ----------------
	# R 1.4.1
> a <- matrix( letters[1:6], 2, 3 )
	# a is a matrix
> print( a )
     [,1] [,2] [,3]
[1,] "a"  "c"  "e" 
[2,] "b"  "d"  "f" 
> b <- sub( '(.)', '-\\1-', a )
	# I had expected b to be a matrix
	# but b is a vector
> print( b )
[1] "-a-" "-b-" "-c-" "-d-"
"-e-" "-f-"

> dim(b) <- dim(a)
> print( b )
	# b is now a matrix again
     [,1]  [,2]  [,3] 
[1,] "-a-" "-c-" "-e-"
[2,] "-b-" "-d-" "-f-"

--------- END OF LOGFILE ----------------



Wolfram Fischer
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Thanks, Andy, for this hint which is easy to implement.

I am just wundering now if there is a reason for this
loss of information about the data structure or if it is
only an inconsistant implementation of a good idea about
matrix operations:
	MATRIX * 10  results in a MATRIX
	paste( MATRIX, "." )  results in a VECTOR
	sub( "a", "A", as.character(MATRIX) )  results in a VECTOR

Wolfram Fischer

-----Original Message-----
From: Liaw, Andy [mailto:andy_liaw at merck.com]
Sent: Friday, May 03, 2002 3:56 PM
To: 'Wolfram Fischer - Z/I/M'
Subject: RE: [R] sub() of matrix returns a vector and not a matrix


`Matrix' in R is just a vector with `dim' attribute.  The sub()
function
(and many others) take a vector as input, and returns a vector.  It
does not
copy any attributes from the input to the output.  You can just as
easily
write a simple wrapper function that adds the dim(b) <- dim(a)
operation.

Andy
> -----Original Message-----
> From: Wolfram Fischer - Z/I/M [mailto:wolfram at fischer-zim.ch]
> Sent: Friday, May 03, 2002 9:16 AM
> To: r-help at stat.math.ethz.ch
> Subject: [R] sub() of matrix returns a vector and not a matrix
>
>
> Is there a simple possibility
> to become directly a matrix
> from a call of sub() on a matrix?
>
>
> --------- START OF LOGFILE ----------------
> 	# R 1.4.1
>
> > a <- matrix( letters[1:6], 2, 3 )
> 	# a is a matrix
> > print( a )
>      [,1] [,2] [,3]
> [1,] "a"  "c"  "e"
> [2,] "b"  "d"  "f"
>
> > b <- sub( '(.)', '-\\1-', a )
> 	# I had expected b to be a matrix
> 	# but b is a vector
> > print( b )
> [1] "-a-" "-b-" "-c-" "-d-"
"-e-" "-f-"
>
>
> > dim(b) <- dim(a)
> > print( b )
> 	# b is now a matrix again
>      [,1]  [,2]  [,3]
> [1,] "-a-" "-c-" "-e-"
> [2,] "-b-" "-d-" "-f-"
>
> --------- END OF LOGFILE ----------------
>
> Wolfram Fischer

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>>>>> "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?


    >> 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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