Process edge attributes from networks graph based on user kwargs

[sriharisundar]

Is your feature request related to a problem? Please describe.

This is my use case - I have a geodataframe with a bunch of linestring geometry. While I can visualize that with geodataframe.hvplot, I do want to show the network topology (arrows etc), so felt ploting a networkx directed graph might be better. So I used momepy.gdf_to_nx. This either returns a DiGraph or a MultiDiGraph, and converts all columns of the gdf to attributes of the graph. For my purposes a DiGraph seems sufficient. I also want to color the edges and show some attributes on hover (thanks to all the posts on ispection policy and hovertools I am able to achieve this). Since there is a geometry attribute in my initial gdf, I get an error when I visualize this graph - TypeError: '<' not supported between instances of 'LineString' and 'LineString'. Entire stack trace is here.

Describe the solution you'd like

I think there are a few ways to get around this, all with some changes in the from_networkx function:

1. Ensure we only parse through types which can be compared (and not avoid just list/dict).
2. Let the user specify edge attributes (as a list and passed in as a kwarg) from the graph to parse into the holoview Graph object.

Additional context

Initially I was using the defaults in momepy.gdf_to_nx and it returns a MultiDiGraph, which stores attributes one level deeper, so supporting that would also involve the keyword approach along with checking the type of graph.

There is a from_networkx function in hvplot.networkx as well as in holoviews graph.py which both seem replicas of each other, so we may have to make changes in the best possible location.

[hoxbro]

Can you share a minimal, reproducible example (MRE)?

In general, a complete script only with the essential code, which can be copied/pasted and immediately run as-is with no modifications.

[sriharisundar]

Here is an MRE. Should I also share my package versions? Thanks!

from shapely.geometry import Point, LineString
import hvplot.networkx as hvnx
import geopandas as gpd
import momepy

d = {'line': ['p1 => p2', 'p2 => p3'], 
     'flow':[10,15], 
     'geometry': [LineString([Point(1,2),Point(2,4)]), LineString([Point(2,4),Point(3,1)])]}
gdf = gpd.GeoDataFrame(d)

graph = momepy.gdf_to_nx(gdf,approach="primal",directed=True,multigraph=False)

edges = hvnx.draw_networkx_edges(
    graph, {n: [n[0], n[1]] for n in list(graph.nodes)}, arrowstyle="->", 
    edge_cmap='viridis', edge_color='flow',colorbar=True
)

edges