how to find maximum and minimum in a matrix

Question

Maryam Hamrahi 2016-8-4

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评论： Maryam Hamrahi 2016-8-4

I have matrix A with n rows and 2 columns. I would like to find rows which has the maximum and/or minimum of X and/or Y. Then, replace zero in these rows.

For instance: I have matrix A and I would like to produce matrix B.

 A= [0.1 0.5
3 0.9
4 0.8
4 0.2
0.7
2 0.6
7 1
2 0.9]
 Here, max. X=1    min. X=0.1     max. Y=1    min. Y=0.2
 B= [0 0
3 0.9
4 0.8
0
0
2 0.6
0
2 0.9]

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Answer 1

Thorsten 2016-8-4

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A= [0.1 0.5
 0.3 0.9
 0.4 0.8
 0.4 0.2
 1 0.7
 0.2 0.6
 0.7 1
 0.2 0.9]
idx = A(:,1)==max(A(:,1)) | A(:,1)==min(A(:,1)) |...
      A(:,2)==max(A(:,2)) | A(:,2)==min(A(:,2));
A(any(idx,2),:) = 0

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Maryam Hamrahi 2016-8-4

I really appreciate your help Thorsten. Thank you very much.

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Answer 2

Stephen23 2016-8-4

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https://ww2.mathworks.cn/matlabcentral/answers/298416-how-to-find-maximum-and-minimum-in-a-matrix#answer_230773

编辑：Stephen23 2016-8-4

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The simplest way would be to use logical indexing:

 >> idx = A==max(A(:)) | A==min(A(:));
 >> A(any(idx,2),:) = 0
 A =
0   0.0
3   0.9
4   0.8
0   0.0
0   0.0
2   0.6
0   0.0
2   0.9

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Stephen23 2016-8-4

编辑：Stephen23 2016-8-4

@Maryam Hamrahi: you are right, I made a mistake, and have now corrected my answer. It should work for you now.

Maryam Hamrahi 2016-8-4

在 MATLAB Online 中打开

Thank you very much Stephen Cobeldick.

your code is working, but it gives me the wrong answer.

I want to have the following:

but it gives me this:

 A =
         0         0
    0.3000    0.9000
    0.4000    0.8000
    0.4000    0.2000
         0         0
    0.2000    0.6000
         0         0
    0.2000    0.9000