website/content/blog/networkxtree.md

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---
title: "Tree-based Plots in NetworkX"
date: 2022-01-02T20:36:41-05:00
draft: false
tags: ["Python"]
math: false
---
A graph in D3 and NetworkX can be represented as a JSON file.
Example:
```json
{
"nodes": [
{"id": 1, "name": "A"},
{"id": 2, "name": "B"},
{"id": 3, "name": "C"}
],
"links": [
{"source": 1,"target": 2},
{"source": 1,"target": 3}
]
}
```
The `nodes` entry in the JSON is a list containing a `node` object. Each `node` object has a unique id and a name which can appear inside the node in the drawing.
The `links` entry in the JSON is a list of `link` objects which each denote a (directed) edge between a source and target id.
To run the following script you'll need `graphwiz` installed on the system. You'll also need to have the python packages `networkx` and `pydot`.
```python
import networkx as nx
from networkx.readwrite import json_graph
from networkx.drawing.nx_pydot import graphviz_layout
import matplotlib.pyplot as plt
# Replace graph_json variable with JSON representation of graph
graph_json = {"nodes": [{"id": 1, "name": "A"},{"id": 2, "name": "B"}],"links": [{"source":1,"target":2}]}
node_labels = {node['id']:node['name'] for node in graph_json['nodes']}
for n in graph_json['nodes']:
del n['name']
g = json_graph.node_link_graph(graph_json, directed=True, multigraph=False)
pos = graphviz_layout(g, prog="dot")
nx.draw(g.to_directed(), pos, labels=node_labels, with_labels=True)
plt.show()
```
Given the JSON from the top of the post it'll produce:
![image-20220103000837137](/files/images/blog/20220103000837137.png)