Filter vertices on several properties - Julia - graph

Question

I am working on julia with the Metagraphs.jl library.
In order to conduct an optimization problem, I would like to get the set/list of edges in the graph that point to a special set of vertices having 2 particular properties in common.
My first guess was to first get the set/list of vertices. But I am facing a first issue which is that the filter_vertices function doesn't seem to accept to apply a filter on more than one property.
Here is below an example of what I would like to do:
g = DiGraph(5)
mg = MetaDiGraph(g, 1.0)
add_vertex!(mg)
add_edge!(mg,1,2)
add_edge!(mg,1,3)
add_edge!(mg,1,4)
add_edge!(mg,2,5)
add_edge!(mg,3,5)
add_edge!(mg,5,6)
add_edge!(mg,4,6)
set_props!(mg,3,Dict(:prop1=>1,:prop2=>2))
set_props!(mg,1,Dict(:prop1=>1,:prop2=>0))
set_props!(mg,2,Dict(:prop1=>1,:prop2=>0))
set_props!(mg,4,Dict(:prop1=>0,:prop2=>2))
set_props!(mg,5,Dict(:prop1=>0,:prop2=>2))
set_props!(mg,6,Dict(:prop1=>0,:prop2=>0))
col=collect(filter_vertices(mg,:prop1,1,:prop2,2))
And I want col to find vertex 3 and no others.
But the filter_vertices would only admit one property at a time and then it makes it more costly to do a loop with 2 filters and then try to compare in order to sort a list with the vertices that have both properties.
Considering the size of my graph I would like to avoid defining this set with multiple and costly loops. Would any one of you have an idea of how to solve this issue in an easy and soft way?
I ended up making this to answer my own question:
fil3=Array{Int64,1}()
fil1=filter_vertices(mg,:prop1,1)
for f in fil1
if get_prop(mg,f,:prop2)==2
push!(fil3,f)
end
end
println(fil3)
But tell me if you get anything more interesting
Thanks for your help!

Answer 1

Please provide a minimal working example in a way we can simply copy and paste, and start right away. Please also indicate where the problem occurs in the code. Below is an example for your scenario:
Pkg.add("MetaGraphs")
using LightGraphs, MetaGraphs
g = DiGraph(5)
mg = MetaDiGraph(g, 1.0)
add_vertex!(mg)
add_edge!(mg,1,2)
add_edge!(mg,1,3)
add_edge!(mg,1,4)
add_edge!(mg,2,5)
add_edge!(mg,3,5)
add_edge!(mg,5,6)
add_edge!(mg,4,6)
set_props!(mg,3,Dict(:prop1=>1,:prop2=>2))
set_props!(mg,1,Dict(:prop1=>1,:prop2=>0))
set_props!(mg,2,Dict(:prop1=>1,:prop2=>0))
set_props!(mg,4,Dict(:prop1=>0,:prop2=>2))
set_props!(mg,5,Dict(:prop1=>0,:prop2=>2))
set_props!(mg,6,Dict(:prop1=>0,:prop2=>0))
function my_vertex_filter(g::AbstractMetaGraph, v::Integer, prop1, prop2)
return has_prop(g, v, :prop1) && get_prop(g, v, :prop1) == prop1 &&
has_prop(g, v, :prop2) && get_prop(g, v, :prop2) == prop2
end
prop1 = 1
prop2 = 2
col = collect(filter_vertices(mg, (g,v)->my_vertex_filter(g,v,prop1,prop2)))
# returns Int[3]
Please check ?filter_vertices --- it gives you a hint on what/how to write to define your custom filter.
EDIT. For filtering the edges, you can have a look at ?filter_edges to see what you need to achieve the edge filtering. Append the below code excerpt to the solution above to get your results:
function my_edge_filter(g, e, prop1, prop2)
v = dst(e) # get the edge's destination vertex
return my_vertex_filter(g, v, prop1, prop2)
end
myedges = collect(filter_edges(mg, (g,e)->my_edge_filter(g,e,prop1,prop2)))
# returns [Edge 1 => 3]

Answer 2

I found this solution:
function filter_function1(g,prop1,prop2)
fil1=filter_vertices(g,:prop1,prop1)
fil2=filter_vertices(g,:prop2,prop2)
filter=intersect(fil1,fil2)
return filter
end
This seems to work and is quite easy to implement.
Just I don't know if the filter_vertices function is taking a lot of computational power.
Otherwise a simple loop like this seems to also work:
function filter_function2(g,prop1,prop2)
filter=Set{Int64}()
fil1=filter_vertices(g,:prop1,prop1)
for f in fil1
if get_prop(g,f,:prop2)==prop2
push!(filter,f)
end
end
return filter
end
I am open to any other answers if you have some more elegant ones.