how to change for loop

I have

    A=[1 ;2; 2; 3; 1]

and

    B=[4; 1; 5; 2 ;3]

then I want to have

C=zeros(size(B),1);
for i =1:size(B,1)
   C(A(i))=B(i);
end

A, B and C are the same size and A contains the indices but not in order. Without a loop, we can do C(A)=B.

Now if I want to have (C is initialized properly at start )

   C=zeros(3,5)

for i =1:size(B,1)
   C(A(i),B(i))=5; %or any other value
end

C(A,B)=5 does not give the expected result. Is the principle not the same?

Answer 1

[Jan]

In C(A,B) the indices defined a block, not the linear index. See:

A = zeros(4, 4);
A(2:3, 2:3) = 1;

This does not insert the ones on the center diagonal elements only, but the indices define all 4 elements in teh center.

To get the same result as for the loop, use:

index    = sub2ind(size(C), A, B)
C(index) = 1

Answer 2

[Roger Stafford]

The assignment C(A) = B will work but first you must set up C as a five-element column vector. It does matter what it initially contains:

C = B; % It could also be C = zeros(5,1);
C(A) = B;

[etudiant_is]

Ok, I wanted to confirm this first. I edited my question according to my real problem.