Find the rows have two same elements from a matrix

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Jiafeng Ye 2022-12-11

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https://ww2.mathworks.cn/matlabcentral/answers/1875917-find-the-rows-have-two-same-elements-from-a-matrix

评论： Torsten 2022-12-11

I have a matrix (each row represents a traingle and each element represents a vertex ID of that traingle), I want to find which two traingles have two same vertices. This question can be demonstrated by the following example, for a matrix like the following:

1 9 8

2 7 8

5 8 9

6 5 4

7 3 8

5 4 8

the output would be [1, 3], [2, 5], and [3, 6], which are the rows have two same elements.

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Jiafeng Ye 2022-12-11

This is not a homework question but a research one.

Each row represents a trainlge (consists of three vertices).

Torsten 2022-12-11

A research is no homework ? Then you don't work at home for your research ?

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Answer 1

Torsten 2022-12-11

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https://ww2.mathworks.cn/matlabcentral/answers/1875917-find-the-rows-have-two-same-elements-from-a-matrix#answer_1125617

编辑：Torsten 2022-12-11

在 MATLAB Online 中打开

A = [1 9 8
     2 7 8
     5 8 9
     6 5 4
     7 3 8
     5 4 8];
[I,J] = meshgrid(1:size(A,1),1:size(A,1));
[rows cols] = find(arrayfun(@(i,j)numel(intersect(A(i,:),A(j,:))),I,J)==2);
tuples = [rows(rows < cols),cols(rows < cols)]
tuples = 4×2
     1     3
     2     5
     3     6
     4     6