3.6.9.1. Measuring Decision Tree performance

Demonstrates overfit when testing on train set.

Get the data

from sklearn.datasets import load_boston
data = load_boston()

Train and test a model

from sklearn.tree import DecisionTreeRegressor
clf = DecisionTreeRegressor().fit(data.data, data.target)

predicted = clf.predict(data.data)
expected = data.target

Plot predicted as a function of expected

from matplotlib import pyplot as plt
plt.figure(figsize=(4, 3))
plt.scatter(expected, predicted)
plt.plot([0, 50], [0, 50], '--k')
plt.axis('tight')
plt.xlabel('True price ($1000s)')
plt.ylabel('Predicted price ($1000s)')
plt.tight_layout()

Pretty much no errors!

This is too good to be true: we are testing the model on the train data, which is not a mesure of generalization.

The results are not valid

Total running time of the script: ( 0 minutes 0.111 seconds)