How to determine blocks in mesh grid?

Question

Xiaohan Du 2016-5-18

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/284875-how-to-determine-blocks-in-mesh-grid

评论： Guillaume 2016-5-19

采纳的回答： Guillaume

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Hello guys,

I have a matrix representing a grid, say

A = [-1 -1; -1 1; 1 -1; 1 1; -1 0; 0 -1; 0 0; 0 1; 1 0];

Every row of A is a Cartesian coordinate. Therefore if you plot a scatter, you'll find that A is a square. My question is: clearly there are four blocks in A: left upper, right upper, left lower, right lower. How can I write a code to generate 4 matrices which each of them represents one block? The result should be something like:

A1 = [-1 -1; 0 -1; -1 0; 0 0], 
A2 = [0 -1; 1 -1; 0 0; 1 0], 
A3 = [-1 0; 0 0; -1 1; 0 1], 
A4 = [0 0; 1 0; 0 1; 1 1].

Thanks!

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Image Analyst 2016-5-19

I think you just did it.

Xiaohan Du 2016-5-19

Hi Image Analyst,

Thanks for the reply!

I know what the answer should be like, and I can do it manually. But with the given matrix, what is the algorithm behind it? What if I have a finer grid? I cannot do it manually forever, it needs to be automatic.

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Answer 1

Guillaume 2016-5-19

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/284875-how-to-determine-blocks-in-mesh-grid#answer_222693

编辑：Guillaume 2016-5-19

在 MATLAB Online 中打开

This should work:

A = [-1 -1; -1 1; 1 -1; 1 1; -1 0; 0 -1; 0 0; 0 1; 1 0];
%get the sorted unique x and y coordinates:
xy = cellfun(@unique, num2cell(A, 1), 'UniformOutput', false);
x = xy{1};
y = xy{2};
%create output
Agrid = cell(numel(y) - 1, numel(x) - 1);
%iterate through the grid and fill output
for xidx = 1 : numel(x) - 1
   for yidx = 1 : numel(y) - 1
      Agrid{yidx, xidx} = [repmat(x(xidx:xidx+1), 2, 1), repelem(y(yidx:yidx+1), 2)];
   end
end