Machine Learning for Beginners in Python: How to Handle Imbalanced Classes In Random Forest

Handle Imbalanced Classes In Random Forest

Preliminaries


/* Load libraries */
from sklearn.ensemble import RandomForestClassifier
import numpy as np
from sklearn import datasets

Load Iris Flower Dataset


/* Load data */
iris = datasets.load_iris()
X = iris.data
y = iris.target

Adjust Iris Dataset To Make Classes Imbalanced


/* Make class highly imbalanced by removing first 40 observations */
X = X[40:,:]
y = y[40:]

/* Create target vector indicating if class 0, otherwise 1 */
y = np.where((y == 0), 0, 1)

Train Random Forest While Balancing Classes

When using RandomForestClassifier a useful setting is class_weight=balanced wherein classes are automatically weighted inversely proportional to how frequently they appear in the data.


/* Create decision tree classifer object */
clf = RandomForestClassifier(random_state=0, n_jobs=-1, class_weight="balanced")

/* Train model */
model = clf.fit(X, y)

 

Python Example for Beginners

Two Machine Learning Fields

There are two sides to machine learning:

  • Practical Machine Learning:This is about querying databases, cleaning data, writing scripts to transform data and gluing algorithm and libraries together and writing custom code to squeeze reliable answers from data to satisfy difficult and ill defined questions. It’s the mess of reality.
  • Theoretical Machine Learning: This is about math and abstraction and idealized scenarios and limits and beauty and informing what is possible. It is a whole lot neater and cleaner and removed from the mess of reality.

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