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

[Alexander Shenkin]

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