sort a matrix in a specific way

Question

LH 2022-11-3

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https://ww2.mathworks.cn/matlabcentral/answers/1842693-sort-a-matrix-in-a-specific-way

评论： LH 2022-11-4

Hi,

I have two matrices that correspond to points coordinates and I want to sort their concatenation in a way illustrated below as following:

%first matrix
A = [0.1 0; 
     0.5 0; 
     1 0.3; 
     1 0.7; 
     0.6 1; 
     0.1 1; 
     0 0.9; 
     0 0.2];
%second matrix
B = [0 0;
     1 0;
     1 1;
     0 1];
%concatenate
C = [A ; B];
%sort matrix C in a way that all cooridnates are sorted in a square-like manner and looks like:
% C = [0 0;
% 0.1 0;
% 0.5 0;
% 1 0;
% 1 0.3;
% 1 0.7;
% 1 1;
% 0.6 1;
% 0.1 1;
% 1 0;
% 1 0.9;
% 0 0.2];

Any help would be appreicted.

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dpb 2022-11-3

I don't really see what is "sorted" about the result??? How did you arrive at that particular permutation?

LH 2022-11-3

All coordinates are in a square-like order. If you imagine you have a square with vertices x=[0 1 1 0] and y[0 0 1 1], then if you have points along its edges, they must be order like matrix C.

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Answer 1

Matt J 2022-11-3

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https://ww2.mathworks.cn/matlabcentral/answers/1842693-sort-a-matrix-in-a-specific-way#answer_1090548

编辑：Matt J 2022-11-3

在 MATLAB Online 中打开

%first matrix
A = [0.1 0; 
     0.5 0; 
     1 0.3; 
     1 0.7; 
     0.6 1; 
     0.1 1; 
     0 0.9; 
     0 0.2];
%second matrix
B = [0 0;
     1 0;
     1 1;
     0 1];
%concatenate
C = [A ; B];
k = convhull(C);
C=C(k,:)
C = 13×2
    0.1000         0
    0.5000         0
    1.0000         0
    1.0000    0.3000
    1.0000    0.7000
    1.0000    1.0000
    0.6000    1.0000
    0.1000    1.0000
         0    1.0000
         0    0.9000

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LH 2022-11-3

Thanks, makes sense. Is there another command/method I can use to do the extact sorting but with keeping all points? If not, I believe coding this will be the only way.

Matt J 2022-11-3

I have given a second answer which should keep all of the points.

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Answer 2

Matt J 2022-11-3

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1842693-sort-a-matrix-in-a-specific-way#answer_1090868

在 MATLAB Online 中打开

A = [0.1 0; 
     0.5 0; 
     1 0.3; 
     1 0.7; 
     0.6 1; 
     0.1 1; 
     0 0.9; 
     0 0.2];
%second matrix
B = [0 0;
     1 0;
     1 1;
     0 1];
%concatenate
C = [A ; B];
D=normalize(C,'center');
[~,k]=sort(atan2(D(:,2),D(:,1)));
C=C(k,:)
C = 12×2
         0    0.2000
         0         0
    0.1000         0
    0.5000         0
    1.0000         0
    1.0000    0.3000
    1.0000    0.7000
    1.0000    1.0000
    0.6000    1.0000
    0.1000    1.0000