Unique quad element list

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:

[madhan ravi]

A minimum working example would help. Explicitly show how your expected result should look like a particular matrix.

[ConvexHull]

See edited post, i have supplied a mat-file.

[ConvexHull]

To generate the minimal example i have applied this to the unique lists. With this i have made the lists non-unique and added random points.

p_quad=[p_quad;p_quad;rand(20,2)];
t_quad=[t_quad;t_quad];

[ConvexHull]

Use this as visualization:

for i_quad=1:size(t_quad,1)
    plot([p_quad(t_quad(i_quad,:),1);p_quad(t_quad(i_quad,1),1)],...
         [p_quad(t_quad(i_quad,:),2);p_quad(t_quad(i_quad,1),2)])
    if(i_quad==1)
        hold on;
    end
end

[ConvexHull]

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

[ConvexHull]

Note that the point ordering inside an element

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

should be preserved.

Answer 1

[ConvexHull]

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(:));

Thanks anyway!