How do I return the indices of randomly sampled matrices?

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virkuz000 2018-5-29

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评论： virkuz000 2018-6-5

Hello. I have two large matrices of equal size. I'm currently using randsample to put randomly selected values of one of the matrices into a new vector. But now I need to also identify the indices of the randomly selected values from the one matrix and correspond it to the same indices in the other matrix.

For example:

A = [1 2 3 4 5; 6 7 8 9 10; 11 12 13 14 15]

B = [16 17 18 19 20; 21 22 23 24 25; 26 27 28 29 30]

If I randomly select from A:

Arand = [3 6 10 1 15 11]

How do I get:

Brand = [18 21 25 16 30 26] where the values of Brand have the same indices in B as Arand has in A?

Do I need to abandon my use of randsample altogether?

Thanks for your help!

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Answer 1

Jeff Miller 2018-5-30

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Especially if A has duplicated scores, it might be better to randomly sample the positions and then take elements of both arrays from those random positions:

nelements = numel(A);
SampleSize = 3;
randices = randsample(1:nelements,SampleSize,false);
randAs = A(randices)
randBs = B(randices)

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virkuz000 2018-6-5

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Answer 2

Paolo 2018-5-29

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编辑：Paolo 2018-5-29

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The following code uses find to search for Arand elements in matrix A, and arrayfun to apply the search for every element in Arand.

The indexes are then used to get the corresponding data from the B matrix.

 %Your inputs.
 A = [1 2 3 4 5; 6 7 8 9 10; 11 12 13 14 15];
 B = [16 17 18 19 20; 21 22 23 24 25; 26 27 28 29 30];
 %Your random sequence.
 Arand = [3 6 10 1 15 11];
 %Get index of position of elements Arand with respect to A.
 index = arrayfun(@(x) find(A==x),Arand);
 %Get B elements at positions specified by index.
 Brand = B(index);