CODEWITHSUNDEEP
arraysmatlabmatrixoctave
user1406177
user1406177

Reputation: 1370

Filling matrix with ones depending on vector

In Octave, I have a vector with indexes e.g. a = [ 1 2 3 1 2 3]. I now want a matrix m = zeros(size(a,2), max(a)) to have ones depending on vector a:

m =
[1 0 0
 0 1 0
 0 0 1
 1 0 0
 0 1 0
 0 0 1]

How do I do that?

I tried this, but it didn't work: m(a,:) = 1;

Upvotes: 0

Views: 66

Answers (2)

simlist
simlist

Reputation: 159

You can also index into an identity matrix like so.

a = [ 1 2 3 1 2 3];

I = eye(max(a));
m = I(a, :);

Upvotes: 0

Dan
Dan

Reputation: 45752

Assuming:

a = [1 2 3 1 2 3];
sz = [numel(a), max(a)];

using sub2ind:

m = zeros(sz);
ind = sub2ind(sz, 1:sz(1), a);
m(ind) = 1;

using sparse

m = full(sparse(1:sz(1), a, 1));

Upvotes: 3

Related Questions