R help - Nov 2010 - translate vector of numbers to indicies of 0/1 matrix

Hello All,

Searched around, haven't found a decent solution.

I'd like to translate a vector of numbers to a matrix (or to a list of
vectors) such that the vector values would serve as indicies of the 1's
in an otherwise-zero-filled matrix (or list of vectors). For example:
> a = c(1,3,3,4)
# perform operation

     [,1] [,2] [,3] [,4]
[1,]    1    0    0    0
[2,]    0    0    1    0
[3,]    0    0    1    0
[4,]    0    0    0    1


Any help greatly appreciated!

thanks,
allie

Alexander -
    If I understand your problem, I think this 
function will make the matrix you want:

makeyourmatrix = function(vec){
    n = length(vec)
    mat = matrix(0,n,n)
    mat[cbind(1:n,vec)] = 1
    mat
}
> makeyourmatrix(c(1,3,3,4))
      [,1] [,2] [,3] [,4]
[1,]    1    0    0    0
[2,]    0    0    1    0
[3,]    0    0    1    0
[4,]    0    0    0    1

 					- Phil Spector
 					 Statistical Computing Facility
 					 Department of Statistics
 					 UC Berkeley
 					 spector at stat.berkeley.edu


On Wed, 17 Nov 2010, Alexander Shenkin wrote:
> Hello All,
>
> Searched around, haven't found a decent solution.
>
> I'd like to translate a vector of numbers to a matrix (or to a list of
> vectors) such that the vector values would serve as indicies of the 1's
> in an otherwise-zero-filled matrix (or list of vectors). For example:
>
>> a = c(1,3,3,4)
>
> # perform operation
>
>     [,1] [,2] [,3] [,4]
> [1,]    1    0    0    0
> [2,]    0    0    1    0
> [3,]    0    0    1    0
> [4,]    0    0    0    1
>
>
> Any help greatly appreciated!
>
> thanks,
> allie
>
> ______________________________________________
> 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.
>

On Nov 17, 2010, at 6:00 PM, Alexander Shenkin wrote:
> Hello All,
>
> Searched around, haven't found a decent solution.
>
> I'd like to translate a vector of numbers to a matrix (or to a list of
> vectors) such that the vector values would serve as indicies of the  
> 1's
> in an otherwise-zero-filled matrix (or list of vectors). For example:
>
>> a = c(1,3,3,4)
>
> # perform operation
>
>     [,1] [,2] [,3] [,4]
> [1,]    1    0    0    0
> [2,]    0    0    1    0
> [3,]    0    0    1    0
> [4,]    0    0    0    1
 > cc <- matrix(0, ncol=max(a), nrow=length(b))
 > cc[matrix(c(1:4, a), ncol=2)] <- 1
# matrix indexing with two column argument
 > cc
      [,1] [,2] [,3] [,4]
[1,]    1    0    0    0
[2,]    0    0    1    0
[3,]    0    0    1    0
[4,]    0    0    0    1

-- 

David Winsemius, MD
West Hartford, CT

On Wed, Nov 17, 2010 at 6:00 PM, Alexander Shenkin <ashenkin at ufl.edu>
wrote:
> Hello All,
>
> Searched around, haven't found a decent solution.
>
> I'd like to translate a vector of numbers to a matrix (or to a list of
> vectors) such that the vector values would serve as indicies of the 1's
> in an otherwise-zero-filled matrix (or list of vectors). For example:
>
>> a = c(1,3,3,4)
>
> # perform operation
>
> ? ? [,1] [,2] [,3] [,4]
> [1,] ? ?1 ? ?0 ? ?0 ? ?0
> [2,] ? ?0 ? ?0 ? ?1 ? ?0
> [3,] ? ?0 ? ?0 ? ?1 ? ?0
> [4,] ? ?0 ? ?0 ? ?0 ? ?1
Try this:

replace(diag(a)*0, cbind(seq_along(a), a), 1)

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