Sorting a list of edges

Hi everybody, I have a list of edges defined as connectivity matrix, that defines a closed loop. For example:

edg = [1 4; 7 4; 8 2; 7 5; 3 8; 1 6; 5 2; 9 6; 3 9 ];

defines a closed loop made of 9 nodes numbered from 1 to 9. These edges are neither sorted nor equi-oriented. Now I would like to sort the edge list starting from the first edge to have an adjacent list of edges. In other words the desired output is

edg_sort = [1 4; 4 7; 7 5; 5 2; 2 8; 8 3; 3 9; 9 6; 6 1];

I was able to find a solution using a for-loop

% preallocate
edg_sort = zeros(size(edg));

% first edge
edg_sort(1,:) = edg(1,:);

% list of visited edges
edg_visited = zeros(size(edg,1),1);
edg_visited(1) = 1;

for i = 2:size(edg,1)
  % node to search for
  inod = edg_sort(i-1,2);

    % indices of edges available
    iedg = find(edg_visited == 0);

    % find node (in local row indexing)
    [idx,jdx] = find(edg(iedg,:) == inod);

    % load new edge: first node
    edg_sort(i,1) = inod;

    % load new edge: second node
    if jdx == 1
        edg_sort(i,2) = edg(iedg(idx),2);
    else
        edg_sort(i,2) = edg(iedg(idx),1);
    end

    % update list of visited edges
    edg_visited(iedg(idx)) = 1;

end

but I wonder whether it is possible to avoid the for-loop, maybe using the adjacency matrix or a similar structure. Any help is appreciated!

Thanks

Fabio

Answer 1

[maryline bawedin]

Hello...Late answer for this post. Here is what I did, a bit shorter code... Below, the variable "RegionEdgeIndex" (1st line) can be your "edg" list

RegionLeftEdgeIndexSorted= sortrows(RegionEdgeIndex, 1);
RegionLeftEdgeIndexSortedTemp= RegionLeftEdgeIndexSorted;
k=1;
RegionEdgeSorted(k,:)= RegionLeftEdgeIndexSortedTemp(1,:); %initialization
RegionLeftEdgeIndexSortedTemp(1,:)=[];
row=1;
while k<=length(RegionEdgeReferenceList)-1
 [row,col] = find(RegionLeftEdgeIndexSortedTemp(:,1)== RegionEdgeSorted(k,2) );
 k=k+1 ;
 RegionEdgeSorted(k,:)=RegionLeftEdgeIndexSortedTemp(row,:)
 RegionLeftEdgeIndexSortedTemp(row,:)=[];
end