[R] Questions on formula in princomp

[Sasha Pustota]

Berton Gunter <gunter.berton at gene.com> wrote:
> plot(myscores[,1:2],pch=c('s','c','v')[groups])

Thanks, this works. How to understand the result of
the expression

   > c(1,2,'3)[groups]
    [1] 3 3 3 3 3 1 1 1 1 1 2 2 2 2 2

where

   > groups <- factor(c(rep("X",5), rep("Y",5), rep("Z",5)))

?

Sorry if it's too basic.