What does R's class.ind() function do and when would I use it?

Question

R documentation says that nnet::class.ind() generates a class indicator function from a given factor.

Does it convert a factor to some binary classification?

When and why do we use this function? Please give me some examples.

Any help appreciated. Thank you.

Answer 1

Yes. It creates indicator/dummy variables from a factor:

> set.seed(1)
> x <- factor(sample(1:3, 10, TRUE))
> nnet::class.ind(x)
      1 2 3
 [1,] 1 0 0
 [2,] 0 1 0
 [3,] 0 1 0
 [4,] 0 0 1
 [5,] 1 0 0
 [6,] 0 0 1
 [7,] 0 0 1
 [8,] 0 1 0
 [9,] 0 1 0
[10,] 1 0 0

It would be essentially the same as using model.matrix:

> model.matrix(~0+x)
   x1 x2 x3
1   1  0  0
2   0  1  0
3   0  1  0
4   0  0  1
5   1  0  0
6   0  0  1
7   0  0  1
8   0  1  0
9   0  1  0
10  1  0  0