Select values of a matrix given a matrix of indices?

Hi, suppose we have a matrix

A=rand(10,10);

Now I have two matrices:

x=[2,3;5,7];  y=[4,6;1,2];

Now I want to create a new matrix

B

where

B(1,1)=A(2,4); B(1,2)=A(3,4); 
B(2,1)=A(5,1); B(2,2)=A(7,2);

is there any fast way to do this?

Answer 1

[Stephen23]

"is there any fast way to do this?"

Use SUB2IND:

A = rand(10,10)

A = 10×10

0.5450 0.4398 0.6459 0.0467 0.0277 0.6175 0.5870 0.0939 0.0574 0.3836 0.0221 0.8333 0.1351 0.9740 0.2953 0.3260 0.2291 0.8171 0.1627 0.5144 0.2870 0.6653 0.1350 0.4574 0.9536 0.2163 0.3253 0.8696 0.7515 0.1564 0.2181 0.7151 0.9130 0.3128 0.5931 0.8399 0.4864 0.9117 0.2175 0.0121 0.2511 0.4902 0.4122 0.5957 0.4164 0.4223 0.1483 0.1979 0.5693 0.3208 0.4414 0.4948 0.7042 0.5923 0.9989 0.6687 0.5911 0.0469 0.9779 0.6344 0.3875 0.1796 0.7852 0.9598 0.3292 0.1749 0.0369 0.5410 0.0619 0.3418 0.1312 0.7621 0.0942 0.8692 0.7387 0.6949 0.4989 0.6069 0.6606 0.0878 0.7811 0.2260 0.5669 0.3541 0.4226 0.1288 0.5321 0.9633 0.0195 0.2571 0.0892 0.5916 0.4890 0.9875 0.5667 0.2207 0.7688 0.8158 0.5442 0.9627

x = [2,3;5,7];
y = [4,6;1,2];
idx = sub2ind(size(A),x,y);
B = A(idx)

B = 2×2

0.9740 0.2163 0.2511 0.1796