New Post

content/blog/networkxtree.md

@@ -0,0 +1,56 @@
+---
+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/20220103000837137.png)
+
+
+