Select values of a matrix given a matrix of indices?

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MementoMori
MementoMori 2023-3-26
编辑： Stephen23 2023-3-26
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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Stephen23
Stephen23 2023-3-26
编辑：Stephen23 2023-3-26
Ran in:
"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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