Changing colors for decision tree plot created using export graphviz

Question

I am using scikit's regression tree function and graphviz to generate the wonderful, easy to interpret visuals of some decision trees:

dot_data = tree.export_graphviz(Run.reg, out_file=None, 
                         feature_names=Xvar,  
                         filled=True, rounded=True,  
                         special_characters=True) 
graph = pydotplus.graph_from_dot_data(dot_data)
graph.write_png('CART.png')
graph.write_svg("CART.svg")

This runs perfectly, but I'd like to change the color scheme if possible? The plot represents CO₂ fluxes, so I'd like to make the negative values green and positive brown. I can export as svg instead and alter everything manually, but when I do, the text doesn't quite line up with the boxes so changing the colors manually and fixing all the text adds a very tedious step to my workflow that I would really like to avoid!

Also, I've seen some trees where the length of the lines connecting nodes is proportional to the % variance explained by the split. I'd love to be able to do that too if possible?

Answer 1

• You can get a list of all the edges via graph.get_edge_list()
• Each source node should have two target nodes, the one with the lower index is evaluated as True, the higher index as False
• Colors can be assigned via set_fillcolor()

import pydotplus
from sklearn.datasets import load_iris
from sklearn import tree
import collections

clf = tree.DecisionTreeClassifier(random_state=42)
iris = load_iris()

clf = clf.fit(iris.data, iris.target)

dot_data = tree.export_graphviz(clf,
                                feature_names=iris.feature_names,
                                out_file=None,
                                filled=True,
                                rounded=True)
graph = pydotplus.graph_from_dot_data(dot_data)

colors = ('brown', 'forestgreen')
edges = collections.defaultdict(list)

for edge in graph.get_edge_list():
    edges[edge.get_source()].append(int(edge.get_destination()))

for edge in edges:
    edges[edge].sort()    
    for i in range(2):
        dest = graph.get_node(str(edges[edge][i]))[0]
        dest.set_fillcolor(colors[i])

graph.write_png('tree.png')

---

Also, i've seen some trees where the length of the lines connecting nodes is proportional to the % varriance explained by the split. I'd love to be able to do that too if possible!?

You could play with set_weight() and set_len() but that's a bit more tricky and needs some fiddling to get it right but here is some code to get you started.

for edge in edges:
    edges[edge].sort()
    src = graph.get_node(edge)[0]
    total_weight = int(src.get_attributes()['label'].split('samples = ')[1].split('<br/>')[0])
    for i in range(2):
        dest = graph.get_node(str(edges[edge][i]))[0]
        weight = int(dest.get_attributes()['label'].split('samples = ')[1].split('<br/>')[0])
        graph.get_edge(edge, str(edges[edge][0]))[0].set_weight((1 - weight / total_weight) * 100)
        graph.get_edge(edge, str(edges[edge][0]))[0].set_len(weight / total_weight)
        graph.get_edge(edge, str(edges[edge][0]))[0].set_minlen(weight / total_weight)