Intergroup edge Id's changes when associated group collapse

Jan 22, 2013 at 9:41 AM
Edited Jan 22, 2013 at 9:44 AM


I am using NodeXL Class Library ( in window form c# application.

In my scenario, i have say two groups in graph g1 and g2

g1 and g2 have some internal edges connection vertices with in their own groups and few intergroup edges that connects the vertices of one group to another.

when i collapse say group g1, It hides all its internal edges and show only intergroup edges to group g2.

At this point of time,  i have tested that intergroup edge id's have been changed. If i again expand the group, the edge id's of those intergroup edges were restored to previous one.

Why it assigning new edge id's to intergroup edges on group collapse ?

Is it a bug ? because we are getting problems at the time we trying to process that intergroup edges as id's were changed on collpase groups.

Jan 22, 2013 at 6:20 PM

That's by design.

When you collapse a group, the vertices in the group are replaced with a new "group vertex."  Something has to be done with the edges that connected the group's vertices with vertices in other groups.  (Those are the intergroup edges.)  An edge's vertices cannot be modified, so what NodeXL does is to clone each intergroup edge, connect the clone to the group vertices, and hide the original edge.  When you expand the group later, the cloned edges are discarded and the original edges are shown again.

You can't tell what's been done when you look at the graph, but that's what's happening under the covers.  And it's why you're seeing a change in edge IDs.

-- Tony

Jan 23, 2013 at 9:01 AM

Thanks :)