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Implement edges function for IGraph #26

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Implement edges function for IGraph #26

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15 changes: 15 additions & 0 deletions src/graph_api.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -34,6 +34,21 @@ end
Base.eltype(::IGraph) = LibIGraph.igraph_int_t
Base.zero(::Type{IGraph}) = IGraph(0)
# Graphs.edges # TODO
function Graphs.edges(g::IGraph)
edge_list = Vector{Graphs.edgetype(g)}()
adjlist = IGAdjList()
LibIGraph.adjlist_init(g,adjlist,LibIGraph.IGRAPH_ALL,LibIGraph.IGRAPH_LOOPS_TWICE,LibIGraph.IGRAPH_MULTIPLE)
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@Krastanov Krastanov Oct 24, 2025

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Good find! This seems like a pretty expensive allocating operation. I would expect there to be a way to iterate over edges without having to create the adjlist.

I suspect this will be a better way: https://igraph.org/c/html/latest/igraph-Iterators.html#edge-iterators

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@Krastanov Krastanov Oct 24, 2025

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and we also need correctness tests

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@subbarayudu8660 subbarayudu8660 Nov 10, 2025

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what do you mean by correctness tests?

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@Krastanov Krastanov Nov 10, 2025

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A new feature usually comes with additions to the test suite, so that one can attest that the feature is correctly implemented. More importantly, such tests will be executed for any change in the future, ensuring that the feature is not accidentally broken.

For instance, here you are implementing an edges function. A convenient correctness test would be some self-consistency check. E.g. create a graph by specifically adding some random set of edges. Then call the edges function on that graph and verify that it returns the same set as the initial set you started with. This type of "round trip" consistency checks are a powerful way to detect issues.

for i in Graphs.vertices(g)
neigh = IGVectorInt(Ref(unsafe_load(adjlist.objref[].adjs,i)))
for k in 1:LibIGraph.vector_int_size(neigh)
j = LibIGraph.vector_int_get(neigh,k-1)+1
if i < j
push!(edge_list,Graphs.SimpleGraphs.SimpleEdge(i,j))
end
end
end
return edge_list
end
Graphs.edgetype(g::IGraph) = Graphs.SimpleGraphs.SimpleEdge{eltype(g)} # TODO maybe expose the edge id information from IGraph
Graphs.has_edge(g::IGraph,s,d) = LibIGraph.get_eid(g,s,d,false,false)[1]!=-1
Graphs.has_vertex(g::IGraph,n::Integer) = 1≤n≤Graphs.nv(g)
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