[R] Annoyance in as.numeric

[Gavin Simpson]

On Mon, 2008-06-16 at 15:35 -0500, markleeds at verizon.net wrote:
> hi: you can do below but i don't know if it's worth it ?
> 
> newx <- data.matrix(data.frame(x))
> print(newx)

That doesn't work Mark:

> str(data.frame(x))
'data.frame':   2 obs. of  2 variables:
 $ X1: Factor w/ 2 levels "1","2": 1 2
 $ X2: Factor w/ 2 levels "3","4": 1 2
> data.matrix(data.frame(x))
     X1 X2
[1,]  1  1
[2,]  2  2

Which is as per documentation - the data.frame() coerces to factors and
data.matrix represents factor by their internal values.

One "solution" might be to save the dims and then reapply:

> mat
     [,1] [,2]
[1,] "1"  "3" 
[2,] "2"  "4" 
> dims <- dim(mat)
> mat2 <- as.numeric(mat)
> dim(mat) <- dims
> mat2
     [,1] [,2]
[1,]    1    3
[2,]    2    4

You could wrap this in a function:

asMatrix <- function(x, ...) {
   dims <- dim(x)
   x <- as.double(x)
   dim(x) <- dims
   return(x)
}

It would be logical to define a method for as.double for matrix objects.
However objects of class "matrix" are not objects in the sense of
isObject() and hence method dispatch will not work in this case.

HTH

G


> 
> 
> On Mon, Jun 16, 2008 at  4:22 PM, Alberto Monteiro wrote:
> 
> > Why does as.numeric convert matrices and arrays to vectors?
> >
> > as.numeric(matrix(c("1", "2", "3", "4"), 2, 2))
> > [1] 1 2 3 4
> >
> > I could only figure out ugly ways to bypass this, like:
> >
> > x <- matrix(c("1", "2", "3", "4"), 2, 2)
> > array(as.numeric(x), dim = dim(x), dimnames = dimnames(x))
> >
> > Alberto Monteiro
> >
> > ______________________________________________
> > R-help at r-project.org mailing list
> > https://stat.ethz.ch/mailman/listinfo/r-help
> > PLEASE do read the posting guide 
> > http://www.R-project.org/posting-guide.html
> > and provide commented, minimal, self-contained, reproducible code.
> 
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
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