networkX：没有兄弟的ego_graph？

Question

I have a directed with no-cycles.networkX graph. I would like to create a subgraph with only all direct or direct predecessors of a given node n. For instance, if n has 3 predecessors, a, b and c, I will also search for predecessors for each of those 3 nodes.

I am currently using the ego_graph method of.networkX, this works perfectly but the output also keeps sibling nodes with no direct access to my target node since it's an directed graph.

def draw(graph_path: Path, target: str, radius: int)
    graph = nx.read_graphml(graphml)
    subgraph = nx.ego_graph(graph, target, undirected=True, radius=radius)
    draw_graph(subgraph, table)

My undirected is set to False because when I set it True , it is only retuning my target only, does not matter what the radius value is.

Target node is called CORE - SUPPLY CHAIN [DEV].20220128 AS_IS stock_V1norm.DIM calendar and with a radius of 1 :

The result is what I am expecting. Now, same target but with a radius of 2 :

The result is not what I was expecting since I am getting sibling and I only wants to get predecessors nodes such as:

graphML sample:

<?xml version='1.0' encoding='utf-8'?>
<graphml xmlns="http://graphml.graphdrawing.org/xmlns" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://graphml.graphdrawing.org/xmlns http://graphml.graphdrawing.org/xmlns/1.0/graphml.xsd">
  <key id="d1" for="node" attr.name="kind" attr.type="string" />
  <key id="d0" for="node" attr.name="zone" attr.type="string" />
  <graph edgedefault="directed">
    <node id="gold_core.customers">
      <data key="d0">gold</data>
      <data key="d1">core</data>>
    </node>
    <node id="rt.F0116">
      <data key="d0">silver</data>>
    </node>
    <node id="hy.F4211">
      <data key="d0">silver</data>
    </node>
    <edge 
      source="hy.F4211"
      target="gold_core.customers"
    />

Answer 1

You can get the predecessors for a node using the DiGraph.predecessors method.

#!/usr/bin/env python
"""
Find predecessors to a given node.
"""
import matplotlib.pyplot as plt
import networkx as nx

from netgraph import Graph # pip install netgraph

# create a test graph
edges = [
    ('parent a', 'target'),
    ('parent b', 'target'),
    ('parent c', 'target'),
    ('grandparent aa', 'parent a'),
    ('grandparent bb', 'parent b'),
    ('grandparent cc', 'parent c'),
    ('parent a', 'sibling'),
    ('target', 'child')
]

g = nx.from_edgelist(edges, create_using=nx.DiGraph)

# get predecessors
parents = list(g.predecessors('target'))
grandparents = []
for parent in parents:
    for grandparent in list(g.predecessors(parent)):
        grandparents.append(grandparent)
predecessors = parents + grandparents

# give predecessors a red color
node_color = dict()
for node in g:
    if node in predecessors:
        node_color[node] = 'red'
    else:
        node_color[node] = 'white'

# plot
fig, (ax1, ax2) = plt.subplots(1, 2)
Graph(g,
      node_layout='dot',
      arrows=True,
      node_color=node_color,
      node_labels=True,
      node_label_fontdict=dict(size=10),
      node_label_offset=0.1,
      ax=ax1
)

# plot subgraph
subgraph = g.subgraph(predecessors + ['target'])
Graph(subgraph,
      node_layout='dot',
      arrows=True,
      node_labels=True,
      node_label_fontdict=dict(size=10),
      node_label_offset=0.1,
      ax=ax2,
)

plt.show()