Error when trying to plot a SimpleWeightedGraph

[adocherty]

This is a nice package for plotting graphs! I'm having some difficulty plotting a SimpleWeightedGraph from SimpleWeightedGraphs.jl and I'm getting an error for some graphs but not others (I'm generating them randomly at the moment).

When I convert the graphs to an unweighted SimpleGraph the plotting works fine, so it seems there is some issue with weighted graphs – but it is inconsistent as some graphs plot and others have an error.

Example code to reproduce the bug:

using Random, LightGraphs, SimpleWeightedGraphs, GraphPlot

Random.seed!(23928)

n_nodes = 10
n_edges = 20

G = SimpleWeightedGraph(n_nodes)
for ii=1:n_edges
    n1 = rand(1:n_nodes)
    n2 = rand(1:n_nodes)
    weight = rand()
    add_edge!(G, n1, n2, weight)
end

gplot(G, layout=spectral_layout)

Running this code I get the following error:

BoundsError: attempt to access 17-element Vector{Vector{Tuple{Float64, Float64}}} at index [18]

Stacktrace:
 [1] setindex!
   @ ./array.jl:839 [inlined]
 [2] graphline(g::SimpleWeightedGraph{Int64, Float64}, locs_x::Vector{Float64}, locs_y::Vector{Float64}, nodesize::Float64)
   @ GraphPlot ~/.julia/packages/GraphPlot/vrIy8/src/lines.jl:73
 [3] gplot(g::SimpleWeightedGraph{Int64, Float64}, locs_x_in::Vector{Float64}, locs_y_in::Vector{Float64}; nodelabel::Nothing, nodelabelc::ColorTypes.RGB{FixedPointNumbers.N0f8}, nodelabelsize::Float64, NODELABELSIZE::Float64, nodelabeldist::Float64, nodelabelangleoffset::Float64, edgelabel::Vector{Any}, edgelabelc::ColorTypes.RGB{FixedPointNumbers.N0f8}, edgelabelsize::Float64, EDGELABELSIZE::Float64, edgestrokec::ColorTypes.RGB{FixedPointNumbers.N0f8}, edgelinewidth::Float64, EDGELINEWIDTH::Float64, edgelabeldistx::Float64, edgelabeldisty::Float64, nodesize::Float64, NODESIZE::Float64, nodefillc::ColorTypes.RGB{FixedPointNumbers.N0f8}, nodestrokec::Nothing, nodestrokelw::Float64, arrowlengthfrac::Float64, arrowangleoffset::Float64, linetype::String, outangle::Float64)
   @ GraphPlot ~/.julia/packages/GraphPlot/vrIy8/src/plot.jl:215
 [4] gplot(g::SimpleWeightedGraph{Int64, Float64}, locs_x_in::Vector{Float64}, locs_y_in::Vector{Float64})
   @ GraphPlot ~/.julia/packages/GraphPlot/vrIy8/src/plot.jl:115
 [5] gplot(g::SimpleWeightedGraph{Int64, Float64}; layout::typeof(spectral_layout), keyargs::Base.Iterators.Pairs{Union{}, Union{}, Tuple{}, NamedTuple{(), Tuple{}}})
   @ GraphPlot ~/.julia/packages/GraphPlot/vrIy8/src/plot.jl:229
 [6] top-level scope
   @ In[6]:1
 [7] eval
   @ ./boot.jl:360 [inlined]
 [8] include_string(mapexpr::typeof(REPL.softscope), mod::Module, code::String, filename::String)
   @ Base ./loading.jl:1094

However, converting to an unweighted SimpleGraph works fine:

gplot(SimpleGraph(G), layout=spectral_layout)

Package versions:
"LightGraphs" => v"1.3.5"
"SimpleWeightedGraphs" => v"1.1.1"
"Compose" => v"0.9.2"
"GraphPlot" => v"0.4.4"

[adocherty]

Update

This is due to the difference in handling of self-loops between SimpleGraphs and SimpleWeightedGraphs, see JuliaGraphs/SimpleWeightedGraphs.jl#53

The graph above has the following edges

1: 1 – 5
2: 2 – 5
3: 1 – 6
4: 2 – 7
5: 3 – 7
6: 5 – 7
7: 6 – 7
8: 1 – 8
9: 2 – 8
10: 3 – 8
11: 4 – 8
12: 5 – 8
13: 7 – 8
14: 4 – 9
15: 8 – 9
16: 3 – 10
17: 9 – 10
18: 10 – 10

SimpleWeightedGraphs reports 17 edges while when converted to a SimpleGraph there are 18 edges (including the self loop).

Solution:
Don't have self-loops in SimpleWeightedGraph or convert to a SimpleGraph for plotting.

[etiennedeg]

fixed by SimpleWeightedGraphs#2