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204.3.10 Pruning a Decision Tree in Python


  • Growing the tree beyond a certain level of complexity leads to overfitting
  • In our data, age doesn’t have any impact on the target variable.
  • Growing the tree beyond Gender is not going to add any value. Need to cut it at Gender
  • This process of trimming trees is called Pruning

Pruning to Avoid Overfitting

  • Pruning helps us to avoid overfitting
  • Generally it is preferred to have a simple model, it avoids overfitting issue
  • Any additional split that does not add significant value is not worth while.
  • We can use Cp – Complexity parameter in R to control the tree growth

Code-Tree Pruning

#We will rebuild a new tree by using above data and see how it works by tweeking the parameteres

dtree = tree.DecisionTreeClassifier(criterion = "gini", splitter = 'random', max_leaf_nodes = 10, min_samples_leaf = 5, max_depth= 5)
DecisionTreeClassifier(class_weight=None, criterion='gini', max_depth=5,
            max_features=None, max_leaf_nodes=10, min_samples_leaf=5,
            min_samples_split=2, min_weight_fraction_leaf=0.0,
            presort=False, random_state=None, splitter='random')
predict3 = dtree.predict(X_train)
[1 1 0 0 0 1 1 1 1 0 0 1 0 0]
predict4 = dtree.predict(X_test)
[1 1 0 0 0 1]
#Accuracy of the model that we created with modified model parameters.
score2 = dtree.score(X_test, y_test)

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