Select values of a matrix given a matrix of indices?

Question

MementoMori 2023-3-26

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1935339-select-values-of-a-matrix-given-a-matrix-of-indices

编辑： Stephen23 2023-3-26

采纳的回答： Stephen23

在 MATLAB Online 中打开

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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Answer 1

Stephen23 2023-3-26

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1935339-select-values-of-a-matrix-given-a-matrix-of-indices#answer_1201054

编辑：Stephen23 2023-3-26

在 MATLAB Online 中打开

"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