Merge pull request #19 from JuliaGraphs/sbromberger/induced

Sbromberger/induced

Author: sbromberger

REQUIRE

@@ -1,3 +1,3 @@
 julia 1.0
-LightGraphs 1.0
+LightGraphs 1.0.2
 JLD2

src/overrides.jl

@@ -1,6 +1,7 @@
 import LightGraphs.LinAlg: adjacency_matrix
+import LightGraphs: induced_subgraph
 
-adjacency_matrix(g::StaticGraph{I,U}, T::DataType; dir = :out) where I<:Integer where U<:Integer =
+adjacency_matrix(g::StaticGraph{I,U}, T::DataType; dir = :out!) where I<:Integer where U<:Integer =
     SparseMatrixCSC{T,I}(nv(g), nv(g), g.f_ind, g.f_vec, ones(T, ne(g)*2))
 
 function adjacency_matrix(g::StaticDiGraph{I,U}, T::DataType; dir = :out) where I<:Integer where U<:Integer
@@ -11,3 +12,52 @@ function adjacency_matrix(g::StaticDiGraph{I,U}, T::DataType; dir = :out) where
     dir != :out && @warn("direction `$dir` not defined for adjacency matrices on StaticGraphs; defaulting to `out`")
     return z
 end
+
+# induced subgraphs preserve the eltypes of the vertices.
+function induced_subgraph(g::StaticDiGraph{I, U}, vlist::AbstractVector{T}) where T <: Integer where I <: Integer where U<:Integer
+    vlist_len = length(vlist)
+    f_vec = Vector{I}()
+    b_vec = Vector{I}()
+    f_ind = Vector{U}([1])
+    b_ind = Vector{U}([1])
+    
+    let vset = I.(vlist) # needed because of julialang/julia/ issue #15276
+        sizehint!(f_ind, vlist_len+1)
+        sizehint!(b_ind, vlist_len+1)
+    
+        vlist_len == length(vset) || throw(ArgumentError("Vertices in subgraph list must be unique"))
+        fpos = 1
+        bpos = 1
+        @inbounds for v in vlist
+            o = filter(x -> x in vset, outneighbors(g, v))
+            i = filter(x -> x in vset, inneighbors(g, v))
+        
+            fpos += length(o)
+            bpos += length(i)
+
+            append!(f_vec, o)
+            append!(b_vec, i)
+            push!(f_ind, fpos)
+            push!(b_ind, bpos)
+        end
+    end
+    return StaticDiGraph(f_vec, f_ind, b_vec, b_ind), T.(vlist)
+end
+
+function induced_subgraph(g::StaticGraph{I, U}, vlist::AbstractVector{T}) where T <: Integer where I <: Integer where U<:Integer
+    vlist_len = length(vlist)
+    f_vec = Vector{I}()
+    f_ind = Vector{U}([1])
+    let vset = I.(vlist) # needed because of julialang/julia/ issue #15276
+        sizehint!(f_ind, vlist_len + 1)
+        vlist_len == length(vset) || throw(ArgumentError("Vertices in subgraph list must be unique"))
+        fpos = 1
+        for v in vlist
+            o = filter(x -> x in vset, outneighbors(g, v))
+            fpos += length(o)
+            append!(f_vec, o)
+            push!(f_ind, fpos)
+        end
+    end
+    return StaticGraph(f_vec, f_ind), T.(vlist)
+end

test/runtests.jl

@@ -53,6 +53,11 @@ const testdir = dirname(@__FILE__)
         @test @inferred !is_directed(StaticGraph)
         @test @inferred collect(edges(hu)) == collect(edges(sg))
 
+        (g1, m1) = @inferred induced_subgraph(hu, [3,2,1])
+        g2 = @inferred hu[3:-1:1]
+        @test g1 == g2
+        @test m1 == [3,2,1]
+
         z = @inferred(adjacency_matrix(hu, Bool, dir=:out))
         @test z[1,2]
         @test !z[1,4]
@@ -107,6 +112,11 @@ const testdir = dirname(@__FILE__)
         @test @inferred is_directed(StaticDiGraph)
         @test @inferred collect(edges(dhu)) == collect(edges(dsg))
 
+        (g1, m1) = @inferred induced_subgraph(dhu, [3,2,1])
+        g2 = @inferred dhu[3:-1:1]
+        @test g1 == g2
+        @test m1 == [3,2,1]
+
         z = @inferred(adjacency_matrix(dhu, Bool, dir=:out))
         @test z[1,2]
         @test !z[2,1]