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Induced bipartite #147

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Induced bipartite #147

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3ec79c5
added support for induced bipartite subgraphs
Codsilla Jun 20, 2022
dc3b24c
added support for DiGraphs
Codsilla Jun 20, 2022
8ed3577
refactor better to match style
Codsilla Jun 21, 2022
21edb53
refactor to better match style
Codsilla Jun 21, 2022
d48860a
included most of the comments made by simonschoelly
Codsilla Jun 21, 2022
bf8f0f6
included most comments made by simonschoelly
Codsilla Jun 21, 2022
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2 changes: 1 addition & 1 deletion src/Graphs.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -55,7 +55,7 @@ MinkowskiCost, BoundedMinkowskiCost,
complement, reverse, reverse!, blockdiag, union, intersect,
difference, symmetric_difference,
join, tensor_product, cartesian_product, crosspath,
induced_subgraph, egonet, merge_vertices!, merge_vertices,
induced_subgraph, induced_bipartite_subgraph, egonet, merge_vertices!, merge_vertices,

# bfs
gdistances, gdistances!, bfs_tree, bfs_parents, has_path,
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34 changes: 34 additions & 0 deletions src/operators.jl
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Expand Up @@ -708,6 +708,40 @@ egonet(g::AbstractGraph{T}, v::Integer, d::Integer, distmx::AbstractMatrix{U}=we
g[neighborhood(g, v, d, distmx, dir=dir)]


"""
induced_bipartite_subgraph(G,X,Y)

Return the bipartite subgraph of `g` induced by the disjoint subsets of vertices X and Y.

"""
function induced_bipartite_subgraph(g::T,X::AbstractVector{U},Y::AbstractVector{U}) where T <: AbstractGraph where U <: Integer
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From convention it would be better to use G instead of T for the graph type. Furthermore, as far as I understand, this method would not work on any kind of AbstractGraph, only on SimpleGraph and SimpleDiGraph. So I would restrict it to these types of graphs.

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I copied the style of induced_subgraph that also uses T for the graph type. If this is more consistent with the convention, I can change it. Also, we could follow what's been done for induced_subgraph which also returns a mapping from the subgraph to the whole graph. This solution would let people use this function for any AbstractGraph (for example, using the mapping to retrieve information in a metagraph)

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I think following induced_subgraph is a good idea for the mapping, for the types I'd go with G


X ∩ Y != [] && throw("X and Y sould not intersect!")
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!(X ⊆ 1:nv(g) && Y ⊆ 1:nv(g)) && throw("X and Y sould be subsets of the vertices")
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unique!(X)
unique!(Y)
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n = length(X) + length(Y)
G = T(n)
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no guarantee this constructor exists (I'm not sure how we solve that though)


newIndex = Dict(reverse.(collect(enumerate([X;Y]))))

for x in X
for y in outneighbors(g,x) ∩ Y
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add_edge!(G,newIndex[x],newIndex[y])
end
end

for y in Y
for x in outneighbors(g,y) ∩ X
add_edge!(G,newIndex[y],newIndex[x])
end
end
G
end



"""
compute_shifts(n::Int, x::AbstractArray)
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9 changes: 9 additions & 0 deletions test/operators.jl
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Expand Up @@ -308,6 +308,7 @@
@test sort(vm) == [1:5;]
end


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useless diff

gs = star_graph(10)
distgs = fill(4.0, 10, 10)
@testset "Egonet: $g" for g in testgraphs(gs)
Expand All @@ -318,6 +319,14 @@
@test @inferred(ndims(g)) == 2
end

g10 = complete_graph(10)
@testset "Induced bipartite Subgraphs: $g" for g in testgraphs(g10)
sg = @inferred(induced_bipartite_subgraph(g, [2,3],[4,5]))
@test nv(sg) == 4
@test ne(sg) == 4
@test is_bipartite(sg)
end
Comment on lines +322 to +328
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@simonschoelly simonschoelly Jun 21, 2022 •
edited
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While this is good, I think we need a few more test cases, e.g.

  • For empty graphs
  • For graphs with self-loops
  • For graphs that are not complete graphs
  • For directed graphs
  • For cases, where an exception is being thrown
  • For U of different type than Int

It might also be good to test more than just some properties, namely if the subgraph is actually the one that we wanted.

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I agree that more tests would be nice


gx = SimpleGraph(100)
@testset "Length: $g" for g in testgraphs(gx)
@test length(g) == 10000
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