induced_subgraph: new method based on a subset of edges (#72)

* induced_subgraph from an edge set

* fixed test_broken for compatibility with julia 1.6

* Remove duplicate code

* Add compat entries for new Aqua tests

---------

Co-authored-by: Guillaume Dalle <[email protected]>

Author: cecileane

Project.toml

@@ -8,9 +8,16 @@ JLD2 = "033835bb-8acc-5ee8-8aae-3f567f8a3819"
 SimpleTraits = "699a6c99-e7fa-54fc-8d76-47d257e15c1d"
 
 [compat]
+Aqua = "0.8"
+BenchmarkTools = "1"
+Documenter = "1"
 Graphs = "1.4.1"
+InteractiveUtils = "1"
 JLD2 = "0.1.11, 0.2, 0.3, 0.4"
+JuliaFormatter = "1"
+MetaGraphs = "0.7"
 SimpleTraits = "0.9"
+Test = "1"
 julia = "1.6"
 
 [extras]

src/graphs.jl

@@ -44,6 +44,7 @@ function Graphs.outneighbors(meta_graph::MetaGraph, code::Integer)
 end
 
 function Base.issubset(meta_graph::MetaGraph, h::MetaGraph)
+    # no checking of: matching vertex label, or matching edge data
     return issubset(meta_graph.graph, h.graph)
 end
 
@@ -267,10 +268,8 @@ function Base.zero(meta_graph::MetaGraph)
     )
 end
 
-function Graphs.induced_subgraph(
-    meta_graph::MetaGraph, vertex_codes::AbstractVector{<:Integer}
-)
-    inducedgraph, code_map = induced_subgraph(meta_graph.graph, vertex_codes)
+function meta_induced_subgraph(meta_graph::MetaGraph, selector)
+    inducedgraph, code_map = induced_subgraph(meta_graph.graph, selector)
     new_graph = MetaGraph(
         inducedgraph,
         empty(meta_graph.vertex_labels),
@@ -284,6 +283,19 @@ function Graphs.induced_subgraph(
     return new_graph, code_map
 end
 
+function Graphs.induced_subgraph(
+    meta_graph::MetaGraph, vertex_codes::AbstractVector{<:Integer}
+)
+    return meta_induced_subgraph(meta_graph, vertex_codes)
+end
+
+function Graphs.induced_subgraph(
+    meta_graph::MetaGraph, edges::AbstractVector{<:AbstractEdge}
+)
+    # separate method to avoid dispatch ambiguity
+    return meta_induced_subgraph(meta_graph, edges)
+end
+
 @traitfn function Graphs.reverse(meta_graph::MG) where {MG <: MetaGraph; IsDirected{MG}}
     edge_data = meta_graph.edge_data
     reverse_edge_data = empty(edge_data)

test/tutorial/2_graphs.jl

@@ -134,7 +134,7 @@ haskey(rock_paper_scissors, :scissors, :rock)
 haskey(reverse(rock_paper_scissors), :scissors, :rock)
 @test haskey(reverse(rock_paper_scissors), :scissors, :rock)  #src
 
-# Finally, let us take a subgraph:
+# Let us take a subgraph induced by a subset of vertices:
 
 rock_paper, _ = induced_subgraph(rock_paper_scissors, [1, 2])
 @test @inferred induced_subgraph(rock_paper_scissors, [1, 2])[1] == rock_paper  #src
@@ -147,3 +147,25 @@ haskey(rock_paper, :paper, :rock)
 #-
 haskey(rock_paper, :rock, :scissors)
 @test !haskey(rock_paper, :rock, :scissors)  #src
+
+# Subgraphs can also be induced by a subset of edges.
+
+subtree_edges = collect(edges(rock_paper_scissors))[2:3]
+rock_paper_scissors_subtree, _ = induced_subgraph(rock_paper_scissors, subtree_edges)
+issubset(rock_paper_scissors_subtree, rock_paper_scissors)
+ne(rock_paper_scissors_subtree)
+@test ne(rock_paper_scissors_subtree) == 2  #src
+#-
+nv(rock_paper_scissors_subtree)
+@test nv(rock_paper_scissors_subtree) == 3  #src
+#-
+[rock_paper_scissors_subtree[e...] for e in edge_labels(rock_paper_scissors_subtree)]
+
+# Checking that a graph is a subset of another is not supported yet. For example, an induced subgraph may appear as not a subset of the original graph, if vertex codes were modified.
+
+issubset(rock_paper_scissors_subtree, rock_paper_scissors)
+@test_broken issubset(rock_paper_scissors_subtree, rock_paper_scissors)  #src
+#-
+rock_scissors, _ = induced_subgraph(rock_paper_scissors, [1, 3])
+issubset(rock_scissors, rock_paper_scissors)
+@test_broken issubset(rock_scissors, rock_paper_scissors)  #src