Intro to XGBoost Models (decision-tree-based ensemble ML Algorithms)

Frank Kane, Sundog Education founder and the author of liveVideo course 📼 Machine Learning, Data Science and Deep Learning with Python | http://mng.bz/gggR 📼 takes a deep dive into one of the most powerful machine learning algorithm, eXtreme Gradient Boosting, using a Jupyter notebook with Python.

✔ To learn more about Hyperparameter Tuning and Machine Learning, Data Science and Deep Learning, check out Frank's liveVideo course: Machine Learning, Data Science and Deep Learning with Python | http://mng.bz/gggR

"Machine Learning, Data Science and Deep Learning with Python" covers machine learning, Tensorflow, artificial intelligence, and neural networks—all skills that are in demand from the biggest tech employers. Filled with examples using accessible Python code you can experiment with, this complete hands-on data science tutorial teaches you techniques used by real data scientists and prepares you for a move into this hot career path.

#python #machinelearning #deeplearning #datascience

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Decision Tree Algorithm..

Decision tree is one of the popular machine learning algorithms which is the stepping stone to understand the ensemble techniques using trees.

Also, Decision Tree algorithm is a hot topic in many of the interviews which are conducted related to data science field.

Understanding Decision Tree…

Decision Tree is more of a kind of Management tool which is used by many professionals to take decisions regarding the resource costs, decision to be made on the basis of filters applied.

The best part of a Decision Tree is that it is a non-parametric tool, which means that there are no underlying assumptions about the distribution of the errors or the data. It basically means that the model is constructed based on the observed data.

They are adaptable at solving any kind of problem at hand (classification or regression). Decision Tree algorithms are referred to as CART (Classification and Regression Trees).

Common terms used with Decision trees:

1. Root Node: It represents entire population or sample and this further gets divided into two or more homogeneous sets.
2. Splitting: It is a process of dividing a node into two or more sub-nodes.
3. Decision Node: When a sub-node splits into further sub-nodes, then it is called decision node.
4. Leaf/ Terminal Node: Nodes do not split is called Leaf or Terminal node.
5. **Max_Depth: **The complete journey of a tree from root till the leaf nodes.
6. Branch / Sub-Tree: A sub section of entire tree is called branch or sub-tree.
7. Parent and Child Node: A node, which is divided into sub-nodes is called parent node of sub-nodes whereas sub-nodes are the child of parent node.

classic example to demonstrate a Decision Tree

How a Decision Tree works!

1. First, we will iterate through all possible splits, calculate the purity of each split and pick the split.
2. The purity is compared across all labels and best is chosen. This makes the root node as best predictor.
3. This algorithm is recursive in nature as the groups formed can be sub-divided and the process is repeated till the tree is fully grown.

Main Decision Areas:

1. Determine the best split:

The node with homogeneous class distribution are preferred.

2. Measures of Node Impurity: Below are the measures of the impurity

(a). Gini Index

(b). Entropy

©. Mis-classification error

Understanding each terminologies with the example:

Let us take a dataset- weather, below is the snapshot of the header of the data:

Now according to the algorithm written above and the decision points to be considered, we need the feature having maximum information split possible.

Note: At the root node, the impurity level will be maximum with negligible information gain. As we go down the tree, the Entropy reduces with maximizing the Information gain.Therefore, we choose a feature with maximum gain achieved.

#data-science #machine-learning #decision-tree #algorithms #algorithms

Decision Tree -Classification

Decision Tree is one of the most widely used machine learning algorithm. It is a supervised learning algorithm that can perform both classification and regression operations.

As the name suggest, it uses a tree like structure to make decisions on the given dataset. Each internal node of the tree represent a “decision” taken by the model based on any of our attributes. From this decision, we can seperate classes or predict values.

Let’s look at both classification and regression operations one by one.

Classification

In Classification, each leaf node of our decision tree represents a **class **based on the decisions we make on attributes at internal nodes.

To understand it more properly let us look at an example. I have used the Iris Flower Dataset from sklearn library. You can refer the complete code on Github — Here.

Image for post

A node’s samples attribute counts how many training instances it applies to. For example, 100 training instances have a petal width ≤ 2.45 cm .

A node’s value attribute tells you how many training instances of each class this node applies to. For example, the bottom-right node applies to 0 Iris-Setosa, 0 Iris- Versicolor, and 43 Iris-Virginica.

And a node’s gini attribute measures its impurity: a node is “pure” (gini=0) if all training instances it applies to belong to the same class. For example, since the depth-1 left node applies only to Iris-Setosa training instances, it is pure and its gini score is 0.

Gini Impurity Formula

where, pⱼ is the ratio of instances of class j among all training instances at that node.

Based on the decisions made at each internal node, we can sketch decision boundaries to visualize the model.

But how do we find these boundaries ?

We use Classification And Regression Tree (CART) to find these boundaries.

CART is a simple algorithm that finds an attribute _k _and a threshold _t_ₖat which we get a purest subset. Purest subset means that either of the subsets contain maximum proportion of one particular class. For example, left node at depth-2 has maximum proportion of Iris-Versicolor class i.e 49 of 54. In the _CART cost function, _we split the training set in such a way that we get minimum gini impurity.The CART cost function is given as:

After successfully splitting the dataset into two, we repeat the process on either sides of the tree.

We can directly implement Decision tree with the help of Scikit learn library. It has a class called DecisionTreeClassifier which trains the model for us directly and we can adjust the hyperparameters as per our requirements.

#machine-learning #decision-tree #decision-tree-classifier #decision-tree-regressor #deep learning

Intro to XGBoost Models (decision-tree-based ensemble ML Algorithms)

Frank Kane, Sundog Education founder and the author of liveVideo course 📼 Machine Learning, Data Science and Deep Learning with Python | http://mng.bz/gggR 📼 takes a deep dive into one of the most powerful machine learning algorithm, eXtreme Gradient Boosting, using a Jupyter notebook with Python.

✔ To learn more about Hyperparameter Tuning and Machine Learning, Data Science and Deep Learning, check out Frank's liveVideo course: Machine Learning, Data Science and Deep Learning with Python | http://mng.bz/gggR

"Machine Learning, Data Science and Deep Learning with Python" covers machine learning, Tensorflow, artificial intelligence, and neural networks—all skills that are in demand from the biggest tech employers. Filled with examples using accessible Python code you can experiment with, this complete hands-on data science tutorial teaches you techniques used by real data scientists and prepares you for a move into this hot career path.

#python #machinelearning #deeplearning #datascience

What are Decision Tree Algorithms? 🌳

This article will cover one of the most advanced algorithms and most widely used in analytical applications. This is an extensive subject, as we have several algorithms and various techniques for working with decision trees.

On the other hand, these algorithms are among the most powerful in Machine Learning and are easy to interpret. So, let’s start by defining what decision trees are and their representation through machine learning algorithms.

For decision tree learning models, we will study some algorithms with C4.5, C5.0, CART, and ID3. In addition, there are some specialized types of decision trees, and we will learn this following the chapter.

The main specialization of decision trees is RandomForest, which is nothing more than a collection of decision trees. We can use RandomForest for attribute selection, i.e., we can use decision trees for Machine Learning models themselves and apply feature selection techniques to prepare our dataset for other machine learning algorithms.

Finally, we will create models, make predictions, study the parameters and pre-processing details of decision trees, and interpret the results of predictive models.

When creating decision trees, we can have trees with lots of branches and leaves, and at some point, we will have to stop the construction of the tree or make adjustments to reduce the number of decision points in the predictive model.

Decision Trees

This machine learning technique is easy to interpret; that is, we can quickly solve the result of a Decision Tree model, RandomForest, or even an Ensemble method, unlike other techniques such as Artificial Neural Networks or Deep Learning challenging to interpret the result.

Decision Trees are known as one of the most powerful and widely used machine learning modeling techniques. Decision Trees can naturally induce rules that can be used for data classification or to make predictions.

A decision tree is a decision support tool. Graphically presents the shape of an upside-down tree, where the root is at the top, and the leaves are at the bottom.

#big-data #machine-learning #programming #artificial-intelligence #algorithms #decision tree

Decision Trees Classifier

Both of Regression Trees and Classification Trees are a part of CART (Classification And Regression Tree) Algorithm. As we mentioned in Regression Trees article, tree is composed of 3-major parts; root-node, decision-node and terminal/leaf-node.

The criteria used here in node splitting differs from that being used in Regression Trees. As before we will run our example and then learn how the model is being trained.

There are three commonly measures are used in the attribute selection Gini impurity measure, is the one used by CART classifier. For more information on these, see Wikipedia.

Data set being used is iris data set

import numpy as np
import pandas as pd
from sklearn.tree import DecisionTreeClassifier
from sklearn.tree import export_graphviz
from six import StringIO  
from IPython.display import Image 
# pip/conda install pydotplus
import pydotplus
from sklearn import datasets
iris = datasets.load_iris()
xList = iris.data  # Data will be loaded as an array
labels = iris.target
dataset = pd.DataFrame(data=xList,
                      columns=iris.feature_names)
dataset['target'] = labels
targetNames = iris.target_names
print(targetNames)
print(dataset)

Iris Flowers

How a Binary Decision Tree Generates Predictions

When an observation or row is passed to a non-terminal node, the row answers the node’s question. If it answers yes, the row of attributes is passed to the leaf node below and to the left of the current node. If the row answers no, the row of attributes is passed to the leaf node below and to the right of the current node. The process continues recursively until the row arrives at a terminal (that is, leaf) node where a prediction value is assigned to the row. The value assigned by the leaf node is the mean of the outcomes of the all the training observations that wound up in the leaf node.

How to split the nodes

Classification trees split a node into two sub-nodes. Splitting into sub-nodes will increase the homogeneity of resultant sub-nodes. In other words, we can say that the purity of the node increases with respect to the target variable. The decision tree splits the nodes on all available variables and then selects the split which results in most homogeneous/pure sub-nodes.

There are major measures being used to determine which attribute/feature is used for splitting and which value within this attribute we will start with. Some of these measures are:

• Gini index (Default in SciKit Learn Classifier).
• Entropy.
• Information gain.

We will start with Gini index measure and try to understand it

Gini Index

Gini index is an impurity measure used to evaluate splits in the dataset. It is calculated by getting the sum of the squared probabilities of each class (target-class) within a certain attribute/feature then benig subtacted from one.

#machine-learning #mls #decision-tree #decision-tree-classifier #classification #deep learning