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

[Gabor Grothendieck]

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)

-- 
Statistics & Software Consulting
GKX Group, GKX Associates Inc.
tel: 1-877-GKX-GROUP
email: ggrothendieck at gmail.com