Creating peculiar vectors and matrices of ones and zeros

Question

John Kim 2016-10-18

编辑： Walter Roberson 2016-10-18

Dear all,

I have a vector of indices, e.g., i = [2, 3, 5].

1. How do I create a vector of length 10, say, v s.t. x = 1 for indices in i, 0 otherwise. Obviously, I can write

x = zeros(10,1); x(i) = 1;

but is there a one liner?

2. How do I create a diagonal matrix of size 10, say, M, s.t. M(k,k) = 1 if k is in i, 0 otherwise. Obviously, I can write

x = zeros(10,1); x(i) = 1; M = diag(x);

but is there a one liner?

I'd appreciate any and all help. Thanks so much!

Best,

John

Answer 1

Walter Roberson 2016-10-18

编辑：Walter Roberson 2016-10-18

ismember(1:10, i)

diag(ismember(1:10,k))

If you were going larger, then you could

sparse(i, i, 1, N, N)

Where N was the size of matrix to use