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Decision Tree in a Cheat Sheet

  • July 05, 2023
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A supervised, non-parametric machine learning technique called a decision tree is utilised for both classification and regression.

Decision Trees are represented as Nodes:

  • Root Node represented as a Rectangle or a Square: or
  • Branch/ Internal Node represented as a Circle:
  • Leaf /Terminal Node represented as a Triangle or a dot: or

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Information Gain:

After the dataset is divided based on an attribute, the information gain is based on the decrease in entropy. It has a value between 0 and 1.

Entropy before - after is the formula for information gain (IG).

Entropy:

It is the measure of impurity, it is also called a measure of uncertainty.

Its value ranges between 0 to 1

Decision Tree in a Cheat Sheet

Gini Index:

The purity is measured by the Gini Index. Gini Index is used by the CART algorithm for decision trees. It has a value between 0 and 1

Decision Tree in a Cheat Sheet

Decision Tree in a Cheat Sheet

  • Stacking: A meta-classifier or a meta-regression is used in the ensemble learning approach known as stacking to merge many classification or regression models.
  • Voting: Voting combines the predictions from multiple machine learning algorithms
  • Hard Voting: The class that gained the most votes in this case will be selected as the output class.
  • Soft Voting: In this, the probability values for each predicted class are added and taken an average, the one with more average is considered.
  • Bagging: Bagging is aggregation in Bootstrap. It improves accuracy and decreases over-fitting.
  • Random Forest: Random Forest is an extension to Bagging. IT minimizes the overfit
  • Ada Boost: Ada Boost seeks to create a powerful classifier by merging many weak classifiers. Improve the weak classifier's accuracy.
  • Gradient Boosting: Gradient Boosting is used to define the loss function and reduce it. It works well with categorical and count data and also handles the missing data well
  • XG Boost: Gradient boosting is improved by XG Boost, which can be applied to both classifiers and regression models.

Decision Tree in a Cheat Sheet

Libraries to install in Python for Decision Tree and Ensemble

  • from sklearn.preprocessing import LabelEncoder - Used for one-hot encoding on the data
  • from sklearn.preprocessing import scale - Data preprocessing for standardization
  • from sklearn.model_selection import train_test_split - To split the data into Train and Test
  • from sklearn.tree import DecisionTreeClassifier as DT - Used in multiclass classification
  • from sklearn import tree - Used to generate and draw trees
  • from sklearn.metrics import accuracy_score - Multilabel classification for subset accuracy
  • from sklearn.metrics import confusion_matrix - Used to evaluate the quality of o/p classifier
  • from sklearn.ensemble import VotingClassifier - Used for prediction based on the most frequent one
  • from sklearn.ensemble import BaggingClassifier - Used on the base classifier on random subsets of the original dataset and aggregate individual predictions
  • from sklearn.ensemble import RandomForestClassifier - Used in both classification and regression models
  • from sklearn.ensemble import AdaBoostClassifier - It uses multiple classifiers to increase the accuracy of the classifier
  • from sklearn.ensemble import GradientBoostingClassifier - Gradient Boosting classifiers is to minimize the loss
  • import xgboost as xgb - XGB is an extension of GB used for speed and performance

 

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Libraries to install in R for Decision Tree and Ensemble

  • library(caTools) -Used for basic utility functions
  • library(C50) - C5.0 classification model for Decision Tree
  • library(rpart) - R implementation in Recursive Partitioning And Regression Trees
  • library(gmodels) - For model fitting
  • library(caret) - For Classification and Regression
  • library(randomForest) - Algorithm for Classification and Regression
  • library(adabag) - AdaBoost for classification with bagging and boosting
  • library(gbm) - Gradient Boosting Machine for Regression models
  • library(xgboost) - It’s an extension to GB and it supports both classification and regression models

 

Hyperparameters in Decision Tree
Hyper Parameters Input Values Default Value
max_depth Integer or None, Optional None
min_samples_split Integer, Float, Optional 2
min_samples_leaf Integer, Float, Optional 1
min_weight_fraction_leaf Float, Optional 0
max_features Integer, Float, string or None, Option None
random_state Integer, RSI or None, Optional None
min_impurity_decrease Float, Optional 0
base_estimator Int Decision Tree
n_estimators Int 10
random_state seed None
n_jobs Int, None None
Criterion Integer, float Gini
min_samples_leaf Integer 1
oob_score Boolean False
learning_rate Integer 1
colsample_byleve Integer, float 1
colsample_bytree Integer, float 1
Subsample Integer, float 1
Eta Integer, float 0.3
min_child_weight Integer 1
Gamma Integer, Float 0
Alpha Integer, float 0
Lambda Integer, float 1

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