Using a matrix as pairs of indexes of another matrix

For instance:

x=[
      1   2   3   4   5   6   7   8   9
     10  20  30  40  50  60  70  80  90
    100 200 300 400 500 600 700 800 900];


% idx are coordinates (row,col) of x array
idx=[1 3 
     2 5
     3 8];
 
for i=1:size(idx,1) % cycle through pairs of idx
 y(i)=x(idx(i,1),idx(i,2));
end

y

y =

3 50 800

How can this be done without a loop?

Answer 1

[Stephen23]

"How can this be done without a loop?"

Using sub2ind, which converts to linear indices:

>> ind = sub2ind(size(x),idx(:,1),idx(:,2));
>> x(ind)
ans =
     3
    50
   800