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
Hi Matteo From assign help page x a variable name, given as a character string. No coercion is done, and the first element of a character vector of length greater than one will be used, with a warning Nothing is said about matrices and dimensions here so I wouldn't expect that assign can operate the way you are expecting. However I am not sure how to do what you want. It has probably something to do with environments which is not my cup of tea. I would do it list way. Here is an example> Named list with 2 matrices> lll<-list(mat_a=mat_a, mat_b=mat_b) > lll$mat_a [,1] [,2] [,3] [,4] [,5] [1,] 0 0 0 0 0 [2,] 0 0 0 0 0 [3,] 0 0 0 0 0 [4,] 0 0 0 0 0 [5,] 0 0 0 0 0 $mat_b [,1] [,2] [,3] [,4] [,5] [1,] 0 0 0 0 0 [2,] 0 0 0 0 0 [3,] 0 0 0 0 0 [4,] 0 0 0 0 0 [5,] 0 0 0 0 0 Name of a matrix> nam[1] "mat_a" Selection of appropriate matrix element and assigning it a value> lll[[which(names(lll)==nam)]][2,2]<-10Changed list> lll$mat_a [,1] [,2] [,3] [,4] [,5] [1,] 0 0 0 0 0 [2,] 0 10 0 0 0 [3,] 0 0 0 0 0 [4,] 0 0 0 0 0 [5,] 0 0 0 0 0 $mat_b [,1] [,2] [,3] [,4] [,5] [1,] 0 0 0 0 0 [2,] 0 0 0 0 0 [3,] 0 0 0 0 0 [4,] 0 0 0 0 0 [5,] 0 0 0 0 0 You can easily put everything in a function similar to yours without using assign. Cheers Petr> -----Original Message----- > From: R-help [mailto:r-help-bounces at r-project.org] On Behalf Of Matteo > Richiardi > Sent: Wednesday, December 23, 2015 9:45 AM > To: r-help at r-project.org > Subject: [R] assigning values to elements of matrixes > > 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 > > ______________________________________________ > R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see > 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.________________________________ Tento e-mail a jak?koliv k n?mu p?ipojen? dokumenty jsou d?v?rn? a jsou ur?eny pouze jeho adres?t?m. 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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
>
> ______________________________________________
> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
> 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.
Dear Matteo,
Here's a function that does what you want and that you should be able to
adapt to your problem. It does have the disadvantage of copying the object twice
(beyond the overhead of assigning to the indexed value):
myassign <- function(x, index, value, envir=.GlobalEnv, ...){
object <- get(x, envir=envir, ...)
object[index] <- value
assign(x, object, envir=envir, ...)
}
Your example:
> a <- 1:4
> myassign("a", 1, 2)
> a
[1] 2 2 3 4
I hope this helps,
John
-----------------------------
John Fox, Professor
McMaster University
Hamilton, Ontario
Canada L8S 4M4
Web: socserv.mcmaster.ca/jfox
> -----Original Message-----
> From: R-help [mailto:r-help-bounces at r-project.org] On Behalf Of Matteo
> Richiardi
> Sent: December 23, 2015 3:45 AM
> To: r-help at r-project.org
> Subject: [R] assigning values to elements of matrixes
>
> 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
>
> ______________________________________________
> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
> 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.
> On Dec 23, 2015, at 12:44 AM, Matteo Richiardi <matteo.richiardi at gmail.com> wrote: > > I am following the example I find on ?assign: > > a <- 1:4 > assign("a[1]", 2)You appear to have completely misinterpreted the intent of the authors of that help page. The next two lines in that example (which you omitted) show that they intended you to see this as a demonstration of what NOT to do: a <- 1:4 assign("a[1]", 2) a[1] == 2 # FALSE get("a[1]") == 2 # TRUE Notice that a[1] was not assigned the value of 2 as demonstrated when the logical test returning FALSE, but that that an object with the pathological name `a[1]` was created.> 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) > }I see that Peter Antoni and John Fox have offered a demonstration of how to use get and assign. Those efforts at macro-ization are essentially recapitulating what happens when using: M_a[5,5] <- value The M_a object is looked up, copied to something named `*tmp*`, and then the assignment within that copy is performed and the value copied back into M_a. These semantics with there attendant inefficiencies have prompted the development of the data.table package where the assignments are done in place. The alternate strategy of Giorgio Garzanio calls to mind this fortune:> fortunes::fortune("parse()")If the answer is parse() you should usually rethink the question. -- Thomas Lumley R-help (February 2005) See pages 11-13 of https://cran.r-project.org/doc/Rnews/Rnews_2001-3.pdf to see how Lumley expands on this theme. -- David.> > 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 > > ______________________________________________ > R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see > 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.David Winsemius Alameda, CA, USA
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 > > > > ______________________________________________ > > R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see > > 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. > >[[alternative HTML version deleted]]