find value in array according to the row and column number

Question

I have two matrix A and B,the first row of matrix A(1,:)=[1 2] refer to the number of row and column matrix B(1,2)=21,now I want to do this work for another rows of matrix A without loops?

A=[1 2;2 3;1 3;3 3];
B=[1 21 34;45 65 87;4 55 66];
for i=1:4
d(i,:)=B(A(i,1),A(i,2))
end
d =[21; 87;34;66] 

Answer 1

An alternative to sub2ind is

d = B(A(:,1)+ (A(:,2)-1)*size(B,1));

Answer 2

Use sub2ind to get linear indices of the required values of B and then use these indices to retrieve those values.

d = B(sub2ind(size(B), A(:,1), A(:,2)));

>> d

d =

    21
    87
    34
    66

Answer 3

I guess the following code must be work for you:

A=[1 2;2 3;1 3;3 3];
B=[1 21 34;45 65 87;4 55 66];
d=diag(B(A(:,1),A(:,2)))