Induced bipartite

src/Graphs.jl

@@ -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,

src/operators.jl

@@ -708,6 +708,43 @@ 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
+
+    X ∩ Y != [] && throw(ArgumentError("X and Y sould not intersect!"))
+    !(X ⊆ vertices(g) && Y ⊆ vertices(g)) && throw(ArgumentError("X and Y should be subsets of the vertices"))
+    !(allunique(X) && allunique(Y)) && throw(ArgumentError("Vertices in subsets of vertices must be unique"))
+
+
+    n = length(X) + length(Y)
+    G = T(n)
+    Y_set = Set(Y)
+    X_set = Set(X)
+
+    newIndex = Dict(reverse.(collect(enumerate([X;Y]))))
+
+    for x in X
+        for y in outneighbors(g,x)
+            (y ∉ Y_set) && continue
+            add_edge!(G,newIndex[x],newIndex[y])
+        end
+    end
+
+    for y in Y
+        for x in outneighbors(g,y)
+            (x ∉ X_set) && continue
+            add_edge!(G,newIndex[y],newIndex[x])
+        end
+    end
+    G
+end
+
+
 
 """
     compute_shifts(n::Int, x::AbstractArray)

test/operators.jl

@@ -308,6 +308,7 @@
         @test sort(vm) == [1:5;]
     end
 
+
     gs = star_graph(10)
     distgs = fill(4.0, 10, 10)
     @testset "Egonet: $g" for g in testgraphs(gs)
@@ -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
+
     gx = SimpleGraph(100)
     @testset "Length: $g" for g in testgraphs(gx)
         @test length(g) == 10000