[R] computing sum of indicator variables

[Uwe Ligges]

Stefan Böhringer wrote:

> My problem is as follows:
> i is a list 

Do you mean a vector?

> of integers of variable length. Now I want to compute a new
> vector/array 

A vector or an array (which dimensions?)?

 > that contains 1's at the positions indicated in i. For
> example:
> c(2, 4) -> c(0, 1, 0, 1)

How long should the result be? max(i)???

If you mean simple vectors in both cases, i's suggest:

   i <- c(2, 4)
   x <- numeric(max(i))
   x[i] <- 1

Uwe Ligges


> Using something like
> i = i - c(0, i[2:length(i) - 1]);
> sapply(i, function(x) c(rep(0, x - 1), 1)));
> 
> faces me with the problem of concatenating the result, which I could
> somehow not find a solution for.
> 
> Thank you very much in advance.
> 
> Stefan
> 
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