added graph_from_edges function

src/Combinatorics/Graphs/functions.jl

@@ -1081,3 +1081,53 @@
     print(io, "$(_to_string(T)) graph with $(nvertices(G)) nodes and $(nedges(G)) edges")
   end
 end
+
+function graph_from_edges(::Type{T},
+  edges::Vector{Edge},
+  n_vertices::Int=-1) where {T <: Union{Directed, Undirected}} 
+
+  n_needed = maximum(reduce(append!,[[src(e),dst(e)] for e in edges]))
+  @req (n_vertices >= n_needed || n_vertices < 0)  "n_vertices must be at least the maximum vertex in the edges"
+
+  g = Graph{T}(max(n_needed, n_vertices))
+  for e in edges
+    add_edge!(g, src(e), dst(e))
+  end
+
+  return g
+end
+
+graph_from_edges(::Type{T},
+edges::EdgeIterator,
+n_vertices::Int=-1) where {T <: Union{Directed, Undirected}} = graph_from_edges(T, collect(edges), n_vertices)
+
+@doc raw"""
+  graph_from_edges(::Type{T}, edges::Vector{Vector{Int}}) where {T <:Union{Directed, Undirected}}
+
+Creates a graph from a vector of edges. Optionally, you could input the number of vertices, but if this number is lower than the maximum vertex in the edges, this argument will be ignored.
+
+# Examples 1
+```jldoctest
+julia> G = graph_from_edges(Undirected, [[1,3],[3,5],[4,5],[2,4],[2,3]])
+Undirected graph with 5 nodes and the following edges:
+(3, 1)(3, 2)(4, 2)(5, 3)(5, 4)
+
+```
+
+```
+# Examples 2
+```jldoctest
+julia> G = graph_from_edges(Undirected,[[1,3]])
+Undirected graph with 3 nodes and the following edges:
+(3, 1))
+
+```
+"""
+graph_from_edges(::Type{T},
+edges::Vector{Vector{Int}},
+n_vertices::Int=-1) where {T <: Union{Directed, Undirected}} = graph_from_edges(T, [Edge(e[1], e[2]) for e in edges], n_vertices)
+
+graph_from_edges(
+edges::Vector{Vector{Int}},
+n_vertices::Int=-1) = graph_from_edges(Undirected, [Edge(e[1], e[2]) for e in edges], n_vertices)
+

src/exports.jl

@@ -585,6 +585,7 @@ export graded_polynomial_ring
 export grading_group
 export graph
 export graph_from_adjacency_matrix
+export graph_from_edges
 export grassmann_pluecker_ideal
 export grid_morphism
 export groebner_basis

test/Combinatorics/Graph.jl

@@ -124,4 +124,19 @@
         g = Graph{Undirected}(1)
         @test !add_edge!(g,1,2)
     end
+
+    @testset "grap_from_edges" begin
+        x1 = [[5,6],[7,8],[11,12]]
+        G1 = graph_from_edges(x1)
+
+        @test nv(G1) == 12
+        @test ne(G1) == 3
+
+        x2 = [[11,3],[3,5],[4,5],[2,4],[2,3]]
+        G2 = graph_from_edges(Undirected, x2, 13)
+
+        @test nv(G2) == 13
+        @test ne(G2) == 5
+
+    end
 end