[R] What's the BEST way in R to adapt this vector?

[hadley wickham]

On Sat, Nov 22, 2008 at 12:00 PM, zerfetzen <zerfetzen at yahoo.com> wrote:
>
> Goal:
> Suppose you have a vector that is a discrete variable with values ranging
> from 1 to 3, and length of 10.  We'll use this as the example:
>
> y <- c(1,2,3,1,2,3,1,2,3,1)
>
> ...and suppose you want your new vector (y.new) to be equal in length to the
> possible discrete values (3) times the length (10), and formatted in such a
> way that if y[1] == 1, then y.new[1:3] == c(1,0,0), and if y[2] == 2, then
> y.new[4:6] == c(0,1,0).  For example, the final goal should be:
>
> y.new <- c(1,0,0,0,1,0,0,0,1,1,0,0,0,1,0,0,0,1,1,0,0,0,1,0,0,0,1,1,0,0)
>
> Note: I know how to do this with loops, but that's not taking advantage of
> R's capabilities with vectors and, I suspect, matrices.

How about:

as.vector(diag(3)[, y])

Hadley

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