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

Phil Spector spector at stat.berkeley.edu
Thu Nov 18 00:08:18 CET 2010

```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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```