R help - Jul 2003 - using cut on matrices

Dear list,

I'd like to use the function cut() on matrices, ie that when I apply
it to a matrix, it would return a matrix of the same dimensions
instead of a vector.

I wonder if there is a better (more elegant) solution than

matrix(cut(a, ...), ncol=ncol(a), nrow=nrow(a))

because I would like to use cut on both vectors and matrices and avoid
testing whether a is a matrix.

Thanks,

Tamas

-- 
Tam?s K. Papp
E-mail: tpapp at axelero.hu (preferred, especially for large messages)
        tpapp at westel900.net
Please try to send only (latin-2) plain text, not HTML or other garbage.

Tamas Papp <tpapp at axelero.hu> writes:
> Dear list,
> 
> I'd like to use the function cut() on matrices, ie that when I apply
> it to a matrix, it would return a matrix of the same dimensions
> instead of a vector.
> 
> I wonder if there is a better (more elegant) solution than
> 
> matrix(cut(a, ...), ncol=ncol(a), nrow=nrow(a))
> 
> because I would like to use cut on both vectors and matrices and avoid
> testing whether a is a matrix.
Will this not work?:

ac <- cut(a)
dim(ac) <- dim(a)

-- 
   O__  ---- Peter Dalgaard             Blegdamsvej 3  
  c/ /'_ --- Dept. of Biostatistics     2200 Cph. N   
 (*) \(*) -- University of Copenhagen   Denmark      Ph: (+45) 35327918
~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk)             FAX: (+45) 35327907

One solution to this problem is to use a function like

Cut <- function(x, ...) {
	m <- match.call()
	m[[1]] <- as.name("cut")
	v <- eval(m, sys.frame(sys.parent()))
	if(is.matrix(x)) matrix(v, nrow(x), ncol(x)) else v
}

but it is an odd sort of thing to want to do.  cut(...) in R produces a
factor result.  If you feed this back into a matrix

matrix(cut(v, breaks = pretty(v)), nrow(v), ncol(v))

you get a character matrix.  

If you adopt Peter's solution below

ac <- cut(a, ......)
dim(ac) <- dim(a)

and a is genuine matrix, you get a factor with a dim attribute which is not
of class matrix.  I found this a bit odd, but don't actually class it as a
bug.  It appears to be another unforseen consequence of the new classes and
methods, I suspect.

Bill Venables.


-----Original Message-----
From: Peter Dalgaard BSA [mailto:p.dalgaard at biostat.ku.dk]
Sent: Saturday, July 12, 2003 8:43 PM
To: tpapp at axelero.hu
Cc: R-help mailing list
Subject: Re: [R] using cut on matrices


Tamas Papp <tpapp at axelero.hu> writes:
> Dear list,
> 
> I'd like to use the function cut() on matrices, ie that when I apply
> it to a matrix, it would return a matrix of the same dimensions
> instead of a vector.
> 
> I wonder if there is a better (more elegant) solution than
> 
> matrix(cut(a, ...), ncol=ncol(a), nrow=nrow(a))
> 
> because I would like to use cut on both vectors and matrices and avoid
> testing whether a is a matrix.
Will this not work?:

ac <- cut(a)
dim(ac) <- dim(a)

-- 
   O__  ---- Peter Dalgaard             Blegdamsvej 3  
  c/ /'_ --- Dept. of Biostatistics     2200 Cph. N   
 (*) \(*) -- University of Copenhagen   Denmark      Ph: (+45) 35327918
~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk)             FAX: (+45) 35327907

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