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etiennedegclaudeKrastanov
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ReverseView and UndirectedView (#376)
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com> Co-authored-by: Stefan Krastanov <github.acc@krastanov.org> Co-authored-by: Stefan Krastanov <stefan@krastanov.org>
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‎docs/make.jl‎

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@@ -44,6 +44,7 @@ pages_files = [
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"core_functions/persistence.md",
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"core_functions/simplegraphs_generators.md",
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"core_functions/simplegraphs.md",
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"core_functions/wrappedgraphs.md",
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],
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"Algorithms API" => [
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"algorithms/biconnectivity.md",

‎docs/src/core_functions/wrappedgraphs.md‎

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# Graph views formats
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*Graphs.jl* provides views around directed graphs.
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`ReverseGraph` is a graph view that wraps a directed graph and reverse the direction of every edge.
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`UndirectedGraph` is a graph view that wraps a directed graph and consider every edge as undirected.
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## Index
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```@index
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Pages = ["wrappedgraphs.md"]
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```
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## Full docs
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```@autodocs
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Modules = [Graphs]
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Pages = [
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"wrappedGraphs/graphviews.jl",
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]
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```

‎src/Graphs.jl‎

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squash,
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weights,
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# wrapped graphs
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ReverseView,
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UndirectedView,
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wrapped_graph,
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# simplegraphs
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add_edge!,
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add_vertex!,
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include("deprecations.jl")
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include("core.jl")
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include("wrappedGraphs/graphviews.jl")
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include("SimpleGraphs/SimpleGraphs.jl")
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using .SimpleGraphs
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"""

‎src/wrappedGraphs/graphviews.jl‎

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"""
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ReverseView{T<:Integer,G<:AbstractGraph} <: AbstractGraph{T}
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A graph view that wraps a directed graph and reverse the direction of every edge.
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!!! warning
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Some properties of the view (e.g. the number of edges) are forwarded from the
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underlying graph and are not recomputed. Modifying the underlying graph after
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constructing the view may lead to incorrect results.
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# Examples
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```jldoctest
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julia> using Graphs
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julia> g = SimpleDiGraph(2);
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julia> add_edge!(g, 1, 2);
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julia> rg = ReverseView(g);
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julia> neighbors(rg, 1)
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Int64[]
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julia> neighbors(rg, 2)
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1-element Vector{Int64}:
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1
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```
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"""
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struct ReverseView{T<:Integer,G<:AbstractGraph} <: AbstractGraph{T}
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g::G
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@traitfn ReverseView{T,G}(g::::(IsDirected)) where {T<:Integer,G<:AbstractGraph{T}} = new(
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g
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)
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@traitfn ReverseView{T,G}(g::::(!IsDirected)) where {T<:Integer,G<:AbstractGraph{T}} = throw(
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ArgumentError("Your graph needs to be directed")
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)
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end
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ReverseView(g::G) where {T<:Integer,G<:AbstractGraph{T}} = ReverseView{T,G}(g)
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wrapped_graph(g::ReverseView) = g.g
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Graphs.is_directed(::ReverseView{T,G}) where {T,G} = true
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Graphs.is_directed(::Type{<:ReverseView{T,G}}) where {T,G} = true
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Graphs.edgetype(g::ReverseView) = Graphs.edgetype(g.g)
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Graphs.has_vertex(g::ReverseView, v) = Graphs.has_vertex(g.g, v)
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Graphs.ne(g::ReverseView) = Graphs.ne(g.g)
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Graphs.nv(g::ReverseView) = Graphs.nv(g.g)
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Graphs.vertices(g::ReverseView) = Graphs.vertices(g.g)
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Graphs.edges(g::ReverseView) = (reverse(e) for e in Graphs.edges(g.g))
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Graphs.has_edge(g::ReverseView, s, d) = Graphs.has_edge(g.g, d, s)
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Graphs.inneighbors(g::ReverseView, v) = Graphs.outneighbors(g.g, v)
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Graphs.outneighbors(g::ReverseView, v) = Graphs.inneighbors(g.g, v)
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"""
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UndirectedView{T<:Integer,G<:AbstractGraph} <: AbstractGraph{T}
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A graph view that wraps a directed graph and consider every edge as undirected.
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!!! warning
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Some properties of the view, such as the number of edges, are cached at
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construction time. Modifying the underlying graph after constructing the view
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will lead to incorrect results.
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# Examples
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```jldoctest
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julia> using Graphs
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julia> g = SimpleDiGraph(2);
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julia> add_edge!(g, 1, 2);
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julia> ug = UndirectedView(g);
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julia> neighbors(ug, 1)
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1-element Vector{Int64}:
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2
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julia> neighbors(ug, 2)
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1-element Vector{Int64}:
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1
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```
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"""
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struct UndirectedView{T<:Integer,G<:AbstractGraph} <: AbstractGraph{T}
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g::G
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ne::Int
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@traitfn function UndirectedView{T,G}(
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g::::(IsDirected)
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) where {T<:Integer,G<:AbstractGraph{T}}
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ne = count(e -> src(e) <= dst(e) || !has_edge(g, dst(e), src(e)), Graphs.edges(g))
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return new(g, ne)
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end
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@traitfn UndirectedView{T,G}(g::::(!IsDirected)) where {T<:Integer,G<:AbstractGraph{T}} = throw(
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ArgumentError("Your graph needs to be directed")
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)
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end
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UndirectedView(g::G) where {T<:Integer,G<:AbstractGraph{T}} = UndirectedView{T,G}(g)
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"""
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wrapped_graph(g)
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Return the graph wrapped by `g`
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"""
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function wrapped_graph end
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wrapped_graph(g::UndirectedView) = g.g
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Graphs.is_directed(::UndirectedView) = false
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Graphs.is_directed(::Type{<:UndirectedView}) = false
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Graphs.edgetype(g::UndirectedView) = Graphs.edgetype(g.g)
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Graphs.has_vertex(g::UndirectedView, v) = Graphs.has_vertex(g.g, v)
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Graphs.ne(g::UndirectedView) = g.ne
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Graphs.nv(g::UndirectedView) = Graphs.nv(g.g)
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Graphs.vertices(g::UndirectedView) = Graphs.vertices(g.g)
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function Graphs.has_edge(g::UndirectedView, s, d)
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return Graphs.has_edge(g.g, s, d) || Graphs.has_edge(g.g, d, s)
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end
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Graphs.inneighbors(g::UndirectedView, v) = Graphs.all_neighbors(g.g, v)
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Graphs.outneighbors(g::UndirectedView, v) = Graphs.all_neighbors(g.g, v)
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function Graphs.edges(g::UndirectedView)
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return (
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begin
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(u, v) = src(e), dst(e)
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if (v < u)
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(u, v) = (v, u)
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end
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Edge(u, v)
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end for
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e in Graphs.edges(g.g) if (src(e) <= dst(e) || !has_edge(g.g, dst(e), src(e)))
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)
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end

‎test/runtests.jl‎

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"interface",
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"core",
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"operators",
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"wrappedGraphs/graphviews",
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"degeneracy",
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"distance",
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"digraph/transitivity",

‎test/wrappedGraphs/graphviews.jl‎

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@testset "Graph Views" begin
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@testset "ReverseView" begin
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gx = DiGraph([
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Edge(1, 1),
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Edge(1, 2),
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Edge(1, 4),
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Edge(2, 1),
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Edge(2, 2),
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Edge(2, 4),
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Edge(3, 1),
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Edge(4, 3),
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])
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gr = erdos_renyi(20, 0.1; is_directed=true)
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for g in hcat(test_generic_graphs(gx), test_generic_graphs(gr))
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rg = ReverseView(g)
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allocated_rg = DiGraph(nv(g))
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for e in edges(g)
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add_edge!(allocated_rg, Edge(dst(e), src(e)))
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end
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@test wrapped_graph(rg) == g
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@test is_directed(rg) == true
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@test eltype(rg) == eltype(g)
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@test edgetype(rg) == edgetype(g)
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@test has_vertex(rg, 4) == has_vertex(g, 4)
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@test nv(rg) == nv(g) == nv(allocated_rg)
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@test ne(rg) == ne(g) == ne(allocated_rg)
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@test all(adjacency_matrix(rg) .== adjacency_matrix(allocated_rg))
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@test sort(collect(inneighbors(rg, 2))) ==
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sort(collect(inneighbors(allocated_rg, 2)))
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@test sort(collect(outneighbors(rg, 2))) ==
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sort(collect(outneighbors(allocated_rg, 2)))
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@test indegree(rg, 3) == indegree(allocated_rg, 3)
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@test degree(rg, 1) == degree(allocated_rg, 1)
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@test has_edge(rg, 1, 3) == has_edge(allocated_rg, 1, 3)
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@test has_edge(rg, 1, 4) == has_edge(allocated_rg, 1, 4)
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rg_res = @inferred(floyd_warshall_shortest_paths(rg))
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allocated_rg_res = floyd_warshall_shortest_paths(allocated_rg)
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@test rg_res.dists == allocated_rg_res.dists # parents may not be the same
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rg_res = @inferred(strongly_connected_components(rg))
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allocated_rg_res = strongly_connected_components(allocated_rg)
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@test length(rg_res) == length(allocated_rg_res)
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@test sort(length.(rg_res)) == sort(length.(allocated_rg_res))
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end
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@test_throws ArgumentError ReverseView(path_graph(5))
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end
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@testset "UndirectedView" begin
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gx = DiGraph([
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Edge(1, 1),
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Edge(1, 2),
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Edge(1, 4),
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Edge(2, 1),
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Edge(2, 2),
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Edge(2, 4),
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Edge(3, 1),
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Edge(4, 3),
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])
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gr = erdos_renyi(20, 0.05; is_directed=true)
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for g in test_generic_graphs(gx)
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ug = UndirectedView(g)
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@test ne(ug) == 7 # one less edge since there was two edges in reverse directions
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end
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for g in hcat(test_generic_graphs(gx), test_generic_graphs(gr))
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ug = UndirectedView(g)
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allocated_ug = Graph(g)
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@test wrapped_graph(ug) == g
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@test is_directed(ug) == false
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@test eltype(ug) == eltype(g)
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@test edgetype(ug) == edgetype(g)
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@test has_vertex(ug, 4) == has_vertex(g, 4)
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@test nv(ug) == nv(g) == nv(allocated_ug)
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@test ne(ug) == ne(allocated_ug)
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@test all(adjacency_matrix(ug) .== adjacency_matrix(allocated_ug))
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@test sort(collect(inneighbors(ug, 2))) ==
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sort(collect(inneighbors(allocated_ug, 2)))
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@test sort(collect(outneighbors(ug, 2))) ==
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sort(collect(outneighbors(allocated_ug, 2)))
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@test indegree(ug, 3) == indegree(allocated_ug, 3)
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@test degree(ug, 1) == degree(allocated_ug, 1)
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@test has_edge(ug, 1, 3) == has_edge(allocated_ug, 1, 3)
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@test has_edge(ug, 1, 4) == has_edge(allocated_ug, 1, 4)
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ug_res = @inferred(floyd_warshall_shortest_paths(ug))
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allocated_ug_res = floyd_warshall_shortest_paths(allocated_ug)
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@test ug_res.dists == allocated_ug_res.dists # parents may not be the same
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ug_res = @inferred(biconnected_components(ug))
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allocated_ug_res = biconnected_components(allocated_ug)
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@test length(ug_res) == length(allocated_ug_res)
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@test sort(length.(ug_res)) == sort(length.(allocated_ug_res))
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end
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@test_throws ArgumentError UndirectedView(path_graph(5))
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end
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end

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