Indices from Max function to Extract Data

Question

Rajesh Rajaram 2015-3-11

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/182650-indices-from-max-function-to-extract-data

评论： Rajesh Rajaram 2015-3-11

I have two arrays:

A=[1 2; 3 2; 3 4];
B=[1 2; 3 4; 5 6];

When I calculate [M,I] = max(A,[],2), I get

Which is fine. Now I want to report values of B for the When A=M in each row; that is:

1
4
5

Is there a way to avoid using the for loop to build my answer array (have a large data set)? I used:

[I_row, I_col] = ind2sub(size(A),I)

but that doesn't seem to help my cause. Kindly help

Thanks in advance

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Andrew Newell 2015-3-11

Your question gets a little garbled in the middle, and I'm not sure what you're after. If you want the values [1 4 5] from B, those correspond to the position of the minima in each row of A. Is that what you want?

Rajesh Rajaram 2015-3-11

So sorry for the confusion. My bad!! I just need the values of B corresponding to the position which has the max values of A.

2 3 6 (and not what I typed. SORRY!!)

I have since found the expression B(sub2ind(size(A), 1:size(A,1), I'))' which seems to do the trick.

But if I want the dim in max function to be changed from 2 to 1, then I have to manually input for sub2ind to get my desired answer.

Is there a generic expression to get the right answer irrespective of the dim that I use in the max function?

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Answer 1

Andrei Bobrov 2015-3-11

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/182650-indices-from-max-function-to-extract-data#answer_170988

编辑：Andrei Bobrov 2015-3-11

在 MATLAB Online 中打开

A=[1 2; 3 2; 3 4];
B=[1 2; 3 4; 5 6];
n = 1;
[~,I]=max(A,[],n);
c ={(1:size(A,3-n))',I(:)}; % EDIT
l = n == 1;
out = B(sub2ind(size(A),c{[l,~l]+[1,1]}));