fix merge_vertices

src/operators.jl

@@ -712,7 +712,7 @@ Determine how many elements of `x` are less than `i` for all `i` in `1:n`.
 """
 function compute_shifts(n::Integer, x::AbstractArray)
  tmp = zeros(eltype(x), n)
- tmp[x[2:end]] .= 1
+ tmp[x] .= 1
  return cumsum!(tmp, tmp)
 end
 
@@ -743,29 +743,25 @@ julia> collect(edges(h))
  Edge 3 => 4
 ```
 """
-function merge_vertices(g::AbstractGraph, vs)
- labels = collect(1:nv(g))
+function merge_vertices(g::AbstractSimpleGraph, vs)
  # Use lowest value as new vertex id.
- sort!(vs)
- nvnew = nv(g) - length(unique(vs)) + 1
+ vs = unique!(sort(vs))
+ merged_vertex = popfirst!(vs)
+
+ nvnew = nv(g) - length(vs)
  nvnew <= nv(g) || return g
- (v0, vm) = extrema(vs)
- v0 > 0 || throw(ArgumentError("invalid vertex ID: $v0 in list of vertices to be merged"))
- vm <= nv(g) || throw(ArgumentError("vertex $vm not found in graph")) # TODO 0.7: change to DomainError?
- labels[vs] .= v0
- shifts = compute_shifts(nv(g), vs[2:end])
- for v in vertices(g)
- if labels[v] != v0
- labels[v] -= shifts[v]
- end
- end
+ merged_vertex > 0 || throw(ArgumentError("invalid vertex ID: $merged_vertex in list of vertices to be merged"))
+ vs[end] <= nv(g) || throw(ArgumentError("vertex $(vs[end]) not found in graph")) # TODO 0.7: change to DomainError?
+
+ new_vertex_ids = collect(vertices(g)) .- compute_shifts(nv(g), vs)
+ new_vertex_ids[vs] .= merged_vertex
 
  #if v in vs then labels[v] == v0 else labels[v] == v
  newg = SimpleGraph(nvnew)
  for e in edges(g)
  u, w = src(e), dst(e)
- if labels[u] != labels[w] #not a new self loop
- add_edge!(newg, labels[u], labels[w])
+ if new_vertex_ids[u] != new_vertex_ids[w] #not a new self loop
+ add_edge!(newg, new_vertex_ids[u], new_vertex_ids[w])
  end
  end
  return newg
@@ -812,35 +808,27 @@ julia> collect(edges(g))
 ```
 """
 function merge_vertices!(g::Graph{T}, vs::Vector{U} where U <: Integer) where T
- vs = sort!(unique(vs))
- merged_vertex = popfirst!(vs)
+ vs = unique!(sort(vs))
+ (merged_vertex, vm) = extrema(vs)
 
- x = zeros(Int, nv(g))
- x[vs] .= 1
- new_vertex_ids = collect(1:nv(g)) .- cumsum(x)
+ merged_vertex > 0 || throw(ArgumentError("invalid vertex ID: $merged_vertex in list of vertices to be merged"))
+ vm <= nv(g) || throw(ArgumentError("vertex $vm not found in graph")) # TODO 0.7: change to DomainError?
+
+ new_vertex_ids = collect(vertices(g)) .- compute_shifts(nv(g), vs[2:end])
  new_vertex_ids[vs] .= merged_vertex
 
  for i in vertices(g)
  # Adjust connections to merged vertices
- if (i != merged_vertex) && !insorted(i, vs)
+ if new_vertex_ids[i] != merged_vertex
  nbrs_to_rewire = Set{T}()
  for j in outneighbors(g, i)
- if insorted(j, vs)
- push!(nbrs_to_rewire, merged_vertex)
- else
- push!(nbrs_to_rewire, new_vertex_ids[j])
- end
+ push!(nbrs_to_rewire, new_vertex_ids[j])
  end
- g.fadjlist[new_vertex_ids[i]] = sort(collect(nbrs_to_rewire))
-
+ g.fadjlist[new_vertex_ids[i]] = sort!(collect(nbrs_to_rewire))
 
  # Collect connections to new merged vertex
  else
  nbrs_to_merge = Set{T}()
- for element in filter(x -> !(insorted(x, vs)) && (x != merged_vertex), g.fadjlist[i])
- push!(nbrs_to_merge, new_vertex_ids[element])
- end
-
  for j in vs, e in outneighbors(g, j)
  if new_vertex_ids[e] != merged_vertex
  push!(nbrs_to_merge, new_vertex_ids[e])
@@ -850,8 +838,9 @@ function merge_vertices!(g::Graph{T}, vs::Vector{U} where U <: Integer) where T
  end
  end
 
+
  # Drop excess vertices
- g.fadjlist = g.fadjlist[1:(end - length(vs))]
+ g.fadjlist = g.fadjlist[begin:(end - length(vs)+1)]
 
  # Correct edge counts
  g.ne = sum(degree(g, i) for i in vertices(g)) / 2

test/operators.jl

@@ -103,6 +103,13 @@
  @test neighbors(h2, 5) == [2]
  @test ne(h2) == 3
  @test nv(h2) == 5
+
+ h3 = star_graph(5)
+ h3merged = merge_vertices(h3, [1,2])
+ @test neighbors(h3merged, 1) == [2,3,4]
+ @test neighbors(h3merged, 2) == [1]
+ @test neighbors(h3merged, 3) == [1]
+ @test neighbors(h3merged, 4) == [1]
  end
  end