# Select values of a matrix given a matrix of indices?

1 view (last 30 days)
MementoMori on 26 Mar 2023
Edited: Stephen23 on 26 Mar 2023
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?

Stephen23 on 26 Mar 2023
Edited: Stephen23 on 26 Mar 2023
"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

### Categories

Find more on Matrix Indexing in Help Center and File Exchange

### Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by