Category Archives: Machine Learning

LabelEncoder Example – Single & Multiple Columns

LabelEncoder for converting labels to integers

In this post, you will learn about LabelEncoder code examples for handling encoding labels related to categorical features of single and multiple columns in Python Pandas Dataframe. The following are some of the points which will get covered: Background What are labels and why encode them? How to use LabelEncoder to encode single & multiple columns (all at once)? When not to use LabelEncoder? Background When working with dataset having categorical features, you come across two different types of features such as the following. Many machine learning algorithms require the categorical data (labels) to be converted or encoded in the numerical or number form. Ordinal features – Features which has …

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Pandas – Fillna method for replacing missing values

Fillna method for replacing missing values

In this post, you will learn about how to use fillna method to replace or impute missing values of one or more feature column with central tendency measures in Pandas Dataframe (Python).The central tendency measures which are used to replace missing values are mean, median and mode. Here is a detailed post on how, what and when of replacing missing values with mean, median or mode. This will be helpful in the data preprocessing stage of building machine learning models. Other technique used for filling missing values is backfill or bfill and forward-fill or ffill. Before going further and learn about fillna method, here is the Pandas sample dataframe we will work with. It represents marks in …

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Python – Replace Missing Values with Mean, Median & Mode

Boxplot for deciding whether to use mean, mode or median for imputation

In this post, you will learn about how to impute or replace missing values  with mean, median and mode in one or more numeric feature columns of Pandas DataFrame while building machine learning (ML) models with Python programming. You will also learn about how to decide which technique to use for imputing missing values with central tendency measures of feature column such as mean, median or mode. This is important to understand this technique for data scientists as handling missing values one of the key aspects of data preprocessing when training ML models. The dataset used for illustration purpose is related campus recruitment and taken from Kaggle page on Campus Recruitment.  As a first step, the …

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Pandas Dataframe vs Numpy Array: What to Use?

Pandas Dataframe vs Numpy Array

In this post, you will learn about which data structure to use between Pandas Dataframe and Numpy Array when working with Scikit Learn libraries. As a data scientist, it is very important to understand the difference between Numpy array and Pandas Dataframe and when to use which data structure. Here are some facts: Scikit learn was originally developed to work well with Numpy array Numpy Ndarray provides a lot of convenient and optimized methods for performing several mathematical operations on vectors. Numpy array can be instantiated using the following manner: np.array([4, 5, 6]) Pandas Dataframe is an in-memory 2-dimensional tabular representation of data. In simpler words, it can be seen …

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Random Forest Classifier Python Code Example

Random forest classifier using python sklearn library

In this post, you will learn about how to train a Random Forest Classifier using Python Sklearn library. This code will be helpful if you are a beginner data scientist or just want to quickly get code sample to get started with training a machine learning model using Random Forest algorithm. The following topics will be covered: Brief introduction of Random Forest Python code example for training a random forest classifier Brief Introduction to Random Forest Classifier Random forest can be considered as an ensemble of several decision trees. The idea is to aggregate the prediction outcome of multiple decision trees and create a final outcome based on averaging mechanism …

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Visualize Decision Tree with Python Sklearn Library

Decision tree visualization using GraphViz

In this post, you will learn about different techniques you can use to visualize decision tree (a machine learning algorithm) using Python Sklearn (Scikit-Learn) library. The python code example would use Sklearn IRIS dataset (classification) for illustration purpose. The decision tree visualization would help you to understand the model in a better manner. The following are two different techniques which can be used for creating decision tree visualisation: Sklearn tree class (plot_tree method) Graphviz library Sklearn Tree Class for Visualization In this section, you will see the code sample for creating decision tree visualization using Sklearn Tree method plot_tree method. Sklearn IRIS dataset is used for training the model. Here is …

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Decision Tree Classifier Python Code Example

Decision tree decision boundaries

In this post, you will learn about how to train a decision tree classifier machine learning model using Python. The following points will be covered in this post: What is decision tree? Decision tree python code sample What is Decision Tree? Simply speaking, the decision tree algorithm breaks the data points into decision nodes resulting in a tree structure. The decision nodes represent the question based on which the data is split further into two or more child nodes. The tree is created until the data points at a specific child node is pure (all data belongs to one class). The criteria for creating the most optimal decision questions is …

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SVM RBF Kernel Parameters with Code Examples

SVM RBF Kernel Parameters - Gamma and C values

In this post, you will learn about SVM RBF (Radial Basis Function) kernel hyperparameters with the python code example.  The following are the two hyperparameters which you need to know while training a machine learning model with SVM and RBF kernel: Gamma  C (also called regularization parameter) Knowing the concepts on SVM parameters such as Gamma and C used with RBF kernel will enable you to select the appropriate values of Gamma and C and train the most optimal model using the SVM algorithm.  Let’s understand why we should use kernel functions such as RBF. Why use RBF Kernel? When the data set is linearly inseparable or in other words, the …

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How to Convert Sklearn Dataset to Dataframe

In this post, you will learn how to convert Sklearn.datasets to Pandas Dataframe. It will be useful to know this technique (code example) if you are comfortable working with Pandas Dataframe. You will be able to perform several operations faster with the dataframe. Sklearn datasets class comprises of several different types of datasets including some of the following: Iris Breast cancer Diabetes Boston Linnerud Images The code sample below is demonstrated with IRIS data set. Before looking into the code sample, recall that IRIS dataset when loaded has data in form of “data” and labels present as “target”. Executing the above code will print the following dataframe. In case, you don’t want to explicitly assign …

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Machine Learning – SVM Kernel Trick Example

In this post, you will learn about what are kernel methods, kernel trick, and kernel functions when referred with a Support Vector Machine (SVM) algorithm. A good understanding of kernel functions in relation to the SVM machine learning (ML) algorithm will help you build/train the most optimal ML model by using the appropriate kernel functions. There are out-of-box kernel functions such as some of the following which can be applied for training models using the SVM algorithm: Polynomial kernel Gaussian kernel Radial basis function (RBF) kernel Sigmoid kernel The following topics will be covered: Background – Why Kernel concept? What is a kernel method? What is the kernel trick? What are …

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How to Know if Data is Linear or Non-linear

Non-linear data set

In this post, you will learn the techniques in relation to knowing whether the given data set is linear or non-linear. Based on the type of machine learning problems (such as classification or regression) you are trying to solve, you could apply different techniques to determine whether the given data set is linear or non-linear. For a data scientist, it is very important to know whether the data is linear or not as it helps to choose appropriate algorithms to train a high-performance model. You will learn techniques such as the following for determining whether the data is linear or non-linear: Use scatter plot when dealing with classification problems Use …

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Sklearn SVM Classifier using LibSVM – Code Example

In this post, you learn about Sklearn LibSVM implementation used for training an SVM classifier, with code example.  Here is a great guide for learning SVM classification, especially, for beginners in the field of data science/machine learning. LIBSVM is a library for Support Vector Machines (SVM) which provides an implementation for the following: C-SVC (Support Vector Classification) nu-SVC epsilon-SVR (Support Vector Regression) nu-SVR Distribution estimation (one-class SVM) In this post, you will see code examples in relation to C-SVC, and nu-SVC LIBSVM implementations. I will follow up with code examples for SVR and distribution estimation in future posts. Here are the links to their SKLearn pages for C-SVC and nu-SVC …

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SVM Classifier using Scikit Learn – Code Examples

In this post, you will learn about how to train an SVM Classifier using Scikit Learn or SKLearn implementation with the help of code examples/samples.  Scikit Learn offers different implementations such as the following to train an SVM classifier.  LIBSVM: LIBSVM is a C/C++ library specialised for SVM. The SVC class is the LIBSVM implementation and can be used to train the SVM classifier (hard/soft margin classifier). Native Python implementation: Scikit Learn provides python implementation of SVM classifier in form SGDClassifier which is based on a stochastic gradient algorithm. LIBSVM SVC Code Example In this section, the code below makes use of SVC class (from sklearn.svm import SVC) for fitting a model. SVM Python Implementation …

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SVM – Understanding C Value with Code Examples

SVM Soft Margin CLassifier and C Value

In this post, we will understand the importance of C value on the SVM soft margin classifier overall accuracy using code samples. In the previous post titled as SVM as Soft Margin Classifier and C Value, the concepts around SVM soft margin classifier and the importance of C value was explained. If you are not sure about the concepts, I would recommend reading earlier article. Lets take a look at the code used for building SVM soft margin classifier with C value. The code example uses the SKLearn IRIS dataset  In the above code example, take a note of the value of C = 0.01. The model accuracy came out to …

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SVM as Soft Margin Classifier and C Value

Soft margin classifier SVM and importance of C value

In this post, you will learn about SVM (Support Vector Machine) as Soft Margin Classifier and the importance of Value of C. In the previous post, we learned about SVM as maximum margin classifier. What & Why of SVM as Soft Margin Classifier? Before getting into understanding what is Soft Margin Classifier version of SVM algorithm, lets understand why we need it when we had a maximum margin classifier. Maximum margin classifier works well with linearly separable data such as the following: When maximum margin classifier is trained on the above data set with maximum distance (margin) between the closest points (support vectors), we can get a hyperplane which can separate the data in a clear …

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SVM Algorithm as Maximum Margin Classifier

SVM as maximum margin classifier

In this post, we will understand the concepts related to SVM (Support Vector Machine) algorithm which is one of the popular machine learning algorithm. SVM algorithm is used for solving classification problems in machine learning.  Lets take a 2-dimensional problem space where a point can be classified as one or the other class based on the value of the two dimensions (independent variables, say) X1 and X2.  The objective is to find the most optimal line (hyperplane in case of 3 or more dimensions) which could correctly classify the points with most accuracy. In the diagram below, you could find multiple such lines possible. In the above diagram, the objective is to find the …

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