[R] Creating Dummy Variables with if else phrase

[Achim Zeileis]

On Friday 02 May 2003 21:41, langensk at fas.harvard.edu wrote:

> Dear All,
>
> I want to do 52 state dummy variables. In order to make it easier
> for me, I thought of using the below commands. (x is the vector with
> state variables, matrix will correspond to the dummy variables)
>
>
> x <- c(1,2,NA,4)
> matrix <- matrix(0,nrow=4,ncol=4)
>
> for (i in 1:4) {
> if (is.real(x[i])) {
> matrix[i,x[i]] <- 1 } else {
> matrix[i,] <- rep(NA,4)
> }
> }
>
> This gives me the following matrix:
>
> 1  0  0  0
> 0  1  0  0
> 0  0  0  0
> 0  0  0  1
>
> But I want it to look as follows:
>
> 1   0  0  0
> 0   1  0  0
> NA NA NA NA
> 0   0  0  1
>

I don't really understand why you want to create a matrix that way, 
but if you want to do it the way described above
  is.real(x[i])
seems to be the wrong function (because x is a real vector in the 
example above). If you want to test for NA you should use
  !is.na(x[i])
instead.
Z

> I want the forth row to be NA, but it is unchanged, i.e., 0. The
> second "else" phrase does not seem to work, and I cannot see what is
> wrong.
>
> I would be very grateful for your help.
>
> Regards, Sophie
>
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