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Machine Learning Algorithms

Machine Learning Algorithms

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Machine Learning Algorithms

Machine Learning Algorithms

Overview of this book

Machine learning has gained tremendous popularity for its powerful and fast predictions with large datasets. However, the true forces behind its powerful output are the complex algorithms involving substantial statistical analysis that churn large datasets and generate substantial insight. This second edition of Machine Learning Algorithms walks you through prominent development outcomes that have taken place relating to machine learning algorithms, which constitute major contributions to the machine learning process and help you to strengthen and master statistical interpretation across the areas of supervised, semi-supervised, and reinforcement learning. Once the core concepts of an algorithm have been covered, you’ll explore real-world examples based on the most diffused libraries, such as scikit-learn, NLTK, TensorFlow, and Keras. You will discover new topics such as principal component analysis (PCA), independent component analysis (ICA), Bayesian regression, discriminant analysis, advanced clustering, and gaussian mixture. By the end of this book, you will have studied machine learning algorithms and be able to put them into production to make your machine learning applications more innovative.
Table of Contents (24 chapters)
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Title Page
Dedication
Packt Upsell
Contributors
Preface
Index

Data scaling and normalization


A generic dataset (we assume here that it is always numerical) is made up of different values that can be drawn from different distributions, having different scales and, sometimes, there are also outliers. A machine learning algorithm isn't naturally able to distinguish among these various situations, and therefore, it's always preferable to standardize datasets before processing them. A very common problem derives from having a non zero mean and a variance greater than 1. In the following graph, there's a comparison between a raw dataset and the same dataset scaled and centered:

Original dataset (left) and the scaled one (right)

This result can be achieved by using the StandardScaler class (which implements feature-wise scaling):

from sklearn.preprocessing import StandardScaler

ss = StandardScaler()
scaled_data = ss.fit_transform(data)

It's possible to specify if the scaling process must include both mean and standard deviation by using the with_mean=True/False...

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