Assign connectivity ID to 2D triangular mesh

This function takes an unrestricted triangulation (only the list of triangles, not the node coordinates) and assigns an ID to each group of triangles. If some cells are connected together, each cell of that group will have the same ID. It works like the connectivity-filter of the graphical library VTK.

function groupID=connectivityTri(TRI)
Input :
"TRI" is mx3 matrix which is the standard list of index of vertices
Output :
"groupID" is mx1 matrix which is the list of ID-group of each cell

Simple example :

X=[2 1 3 2 5 5 8 6 7 5 8 9 10 12 10 12 13 15 1 0 2 1];
Y=[2 4 4 6 6 8 8 4 2 2 4 6 8 7 5 5 3 2 7 8 8 9];
Z=zeros(size(X));
TRI=[1 2 3;2 4 3;4 3 5;5 6 7;10 8 9;8 9 11;12 13 14;15 16 17;17 16 18;4 6 5;20 19 21;22 21 20];
groupID=connectivityTri(TRI);

trisurf(TRI,X,Y,Z,groupID) (the screenshot of the soumission)