Unique quad element list

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ConvexHull 2020-7-8

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/561521-unique-quad-element-list

编辑： ConvexHull 2020-7-8

采纳的回答： ConvexHull

example.mat

在 MATLAB Online 中打开

Dear all,

i am stuck with a small (easy) problem and need a hint.

Consider you have a non-unique element list t_quad with size(n_quad,4) and a corresponding non-unique point list p_quad with size(n_points,2).

Moreover, the point list also contains points which are never indexed by the element list.

I want to make both lists unique meaning i want to have a t_quad_unique list and a p_quad_unique list:

% Works!: This removes the non-unique elements and the corresponding points
[t_quad,~,~]=unique(t_quad,'rows');
[p_quad,~,b]=unique(p_quad,'rows');
t_quad(:)=b(t_quad(:));

Then after this i want to remove also the non-used points which are never used by the element list:

% Does not work!
[p_quad,~,b]=unique(p_quad(t_quad(:),:),'rows');
t_quad(:)=b(t_quad(:));

I lose some informations in this step. Where is the mistake?

Thanks for your help!

Edit:

Before:

After:

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ConvexHull 2020-7-8

编辑：ConvexHull 2020-7-8

Note that the minimal example is quite specific. The non-used random points may be located arbitrary in the point list.

ConvexHull 2020-7-8

编辑：ConvexHull 2020-7-8

Note that the point ordering inside an element

t_quad(:,1) --> t_quad(:,2) --> t_quad(:,3) --> t_quad(:,4)

should be preserved.

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采纳的回答

ConvexHull 2020-7-8

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/561521-unique-quad-element-list#answer_462869

编辑：ConvexHull 2020-7-8

在 MATLAB Online 中打开

I answer my own question. This should work:

[t_quad,~,~]=unique(t_quad,'rows');
[p_quad,~,b]=unique(p_quad,'rows');
t_quad(:)=b(t_quad(:));
[p_unique,~,~]=unique(p_quad(t_quad(:),:),'rows');
[~,c]=ismember(p_quad,p_unique,'rows');
p_quad=p_unique;
t_quad(:)=c(t_quad(:));