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Random Forest Algorithm
Sneha Bose
2 years ago
Table of Content
- Why do we use a Random Forest Algorithm?
- How does Random forest works?
- Advantages of Random Forest:
- Disadvantages of Random Forest:
- Implementation in Python
- Summary
Random Forest algorithm is an ensemble model that uses “Bagging” as the ensemble method and decision tree as
the individual model. It is a learning method that works by constructing
multiple decision trees and the final decision is made based on the majority of
the trees and is chosen by the random forest.
The random forest comes under supervised learning and can be
used for both classification as well as regression problems. But mostly, it is
used for classification problems.
A decision tree algorithm is a tree-shaped diagram which
is used to determine a course of action. In decision tree, each branch of the
tree represents a possible decision, occurrence, or reaction.
Why do we use a Random Forest Algorithm?
One of the main advantages of using Random Forest The algorithm among a lot of benefits is that it reduces the risk of overfitting
and as well as the required training time. Additionally, it provides a high
level of accuracy. Random Forest algorithm runs efficiently in large datasets
and also produces highly accurate predictions by estimating missing data.
How does Random forest works?
·
Step
1 - Select n (e.g.
1500) random subsets from the training set.
·
Step
2 - Train “n”
decision trees. (Here, 1500 for 1 each)
·
Step
3 - Each
individual tree predicts the records/candidates in the train set,
independently.
·
Step
4 - Make the final
predictions using the majority voting.
Advantages of Random Forest:
1. The
random-forest can solve both types of problems that are classification and
regression and does a decent estimation on both fronts.
2. One
of the benefits of Random Forest which exists me most is the power to handle
large data sets with higher dimensionality. It can handle thousands of input
variables and identify the most significant variables so it is considered as one of
the dimensionality reduction methods. Furthermore, the model outputs the
importance of variable, which can be a very handy feature for feature
selection.
3. It
has an effective method for estimating missing data and maintains accuracy when a large proportion of the data is missing.
4. It
has methods for balancing errors in data sets where classes are imbalanced.
5. The capability of the above can be extended to unlabeled data, leading to
unsupervised clustering, data views, and outlier detection.
6. Random
forest involves the sampling of the input data with a replacement called
bootstrap sampling. Here one-third of data is not used for training and can be
used for testing. These are called the OUT OF BAG samples. The Error estimated
on these output bag samples is known as OUT OF BAG ERROR. The study of error
estimates by out of the bag provides us evidence to show that the out of bag
estimate is as accurate as using a test set of the same size as the training
set. Therefore, using the out of bag error estimate helps us to remove the need
for a set-aside test set.
Disadvantages of Random Forest:
1. It
surely does a good job at classification but not as for regression problem as
it does not give precise continuous nature prediction. In the case of regression,
it doesn't predict beyond the range in the training data, and that they may
overfit data sets that are particularly noisy.
2. The
random-forest can feel like a black box approach for a statistical modeler we
have very little control over what the model does. You can at best try different
parameters and random seeds.
Implementation in Python
Let’s
see how we can implement the Random forest algorithm in Python. For this, we will be
taking the Iris dataset.
# Importing libraries
import numpy as np
import matplotlib.pyplot as plt
import pandas as pd
# dataset path link
data_path = “https://archive.ics.uci.edu/ml/machine-learning-databases/iris/iris.data”
# Providing dataset headers
headers = ['sepal-length', 'sepal-width', 'petal-length', 'petal-width', 'Class']
#Loading and printing dataframe
dataset = pd.read_csv(data_path, names = headers)
dataset.head()
# Assigning independent and dependent variables (target variable)
X = dataset.iloc[:, :-1].values #(independent variable)
y = dataset.iloc[:, 4].values #(dependent variable)
#splitting dataset into the ratio of 80:20
from sklearn.model_selection import train_test_split
X_train, X_test, y_train, y_test = train_test_split(X, y, test_size = 0.20)
# Training the Random forest model
from sklearn.ensemble import RandomForestClassifier
classifier = RandomForestClassifier(n_estimators = 50)
classifier.fit(X_train, y_train)
#Making predictions
y_pred = classifier.predict(X_test)
# Printing the result
from sklearn.metrics import classification_report, confusion_matrix, accuracy_score
result = confusion_matrix(y_test, y_pred)
print(“confusion Matrix:”)
result1 = classification_report(y_test, y_pred)
print(“Classification Report:”)
print(result1)
result2 = accuracy_score(y_test, y_pred)
print(“Accuray:”, result2)
Output
Confusion Matrix:
[[14 0 0]
[ 0 18 1]
[ 0 0 12]]
Classification Report:
precision recall f1-score support
Iris-setosa 1.00 1.00 1.00 14
Iris-versicolor 1.00 0.95 0.97 19
Iris-virginica 0.92 1.00 0.96 12
micro avg 0.98 0.98 0.98 45
macro avg 0.97 0.98 0.98 45
weighted avg 0.98 0.98 0.98 45
Accuracy: 0.9777777777777777
SUMMARY
In this articles we learnt about Random Forest Algorithm, Advantages and Disadvantages of Random Forest Algorithm, and its implementation in python.
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