[R] translate vector of numbers to indicies of 0/1 matrix

[Phil Spector]

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
>
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