Some canned algorithms in libgalois modify the PropertyGraph they are passed

[arthurp]

Several algorithms modify the graph they are passed. Specifically they relabel nodes and edges. This is a pretty serious issue since it is not an expected behavior for an algorithm to just randomly rename things.

Currently this affects:

• K-truss
• Local clustering coefficient

You can search for my TODOs with: https://github.com/KatanaGraph/katana/search?q=%22Don%27t+mutate+the+users+topology%22

The long term solution to this is complex because it will require something like this (as pseudo-code; these functions don't exist.):

# Create our working copy of the graph
working_pg = pg.Copy()
# Relabel nodes and edges as needed
permutation = RelabelThings(working_pg)
# Run the actual algorithm
RunAlgorithm(working_pg, output_properties)
# Copy the output properties back to the original graph, reverting the permutation.
pg.AddProperties(PermuteProperties(working_pg, output_properties, permutation))

Though as RDGs mature, the ideal would be having a lazily constructed relabel of the graph that is created and then cached between algorithm runs. We would still need some support for moving/reordering properties between different relabels of graphs.