[R] assigning values to elements of matrixes
Matteo Richiardi
matteo.richiardi at gmail.com
Thu Dec 24 20:18:31 CET 2015
Dear all,
Thanks very much for your help. This completely clarifies my question.
Mayteo
Il giorno 23/dic/2015 17:05, "Anthoni, Peter (IMK)" <peter.anthoni at kit.edu>
ha scritto:
> Hi,
>
> How about the following:
> foo2 <- function(s,i,j,value)
> {
> M = get(paste("M_",s,sep=""))
> M[i,j] = value
> assign(paste("M_",s,sep=""),M, envir = .GlobalEnv)
> }
>
> foo2("a",1,2,15)
>
> cheers
> Peter
>
> > On 23 Dec 2015, at 09:44, Matteo Richiardi <matteo.richiardi at gmail.com>
> wrote:
> >
> > I am following the example I find on ?assign:
> >
> > a <- 1:4
> > assign("a[1]", 2)
> >
> > This appears to create a new variable named "a[1]" rather than
> > changing the value of the vector.
> >
> > Am I missing something here? How can I assign a value to a specified
> > element of a vector/matrix?
> >
> > Of course, my problem is slightly more involved, but I guess the above
> > is its core. For those interested, I have the two matrixes
> > M_a <- matrix(0,10,10)
> > M_b <- matrix(0,10,10)
> >
> > I want to have a function that assigns a value to a specific element
> > of one of the matrix, as in
> > foo <- function(s,i,j,value){
> > assign(paste("M_",s)[i,j],value)
> > }
> >
> > This however does not work:
> >
> > foo('a',1,1,1)
> >
> > Error in paste("M_", s)[1, j] : incorrect number of dimensions
> >
> > Following the ?assign help, I tried
> >
> > foo2 <- function(s,i,j,value){
> > assign(paste("M_",s,"[i,j]"),value, envir = .GlobalEnv)
> > }
> >
> > but this produces the problem I described above (namely, a new
> > variable is created, rather than replacing the specified element of
> > the matrix).
> >
> > I know that in this example I could simply pass the matrix as an
> > argument to the function, but I am interested in understanding how
> > 'assign' work.
> >
> > Many thanks for your help.
> >
> > Matteo
> >
> > ______________________________________________
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> > 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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