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

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MementoMori il 26 Mar 2023
Modificato: Stephen23 il 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?
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### Risposta accettata

Stephen23 il 26 Mar 2023
Modificato: Stephen23 il 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
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