#### Overview of this book

Data Science with R aims to teach you how to begin performing data science tasks by taking advantage of Rs powerful ecosystem of packages. R being the most widely used programming language when used with data science can be a powerful combination to solve complexities involved with varied data sets in the real world. The book will provide a computational and methodological framework for statistical simulation to the users. Through this book, you will get in grips with the software environment R. After getting to know the background of popular methods in the area of computational statistics, you will see some applications in R to better understand the methods as well as gaining experience of working with real-world data and real-world problems. This book helps uncover the large-scale patterns in complex systems where interdependencies and variation are critical. An effective simulation is driven by data generating processes that accurately reflect real physical populations. You will learn how to plan and structure a simulation project to aid in the decision-making process as well as the presentation of results. By the end of this book, you reader will get in touch with the software environment R. After getting background on popular methods in the area, you will see applications in R to better understand the methods as well as to gain experience when working on real-world data and real-world problems.
Simulation for Data Science with R
Credits
www.PacktPub.com
Preface
Free Chapter
Introduction
R and High-Performance Computing
The Discrepancy between Pencil-Driven Theory and Data-Driven Computational Solutions
Simulation of Random Numbers
Monte Carlo Methods for Optimization Problems
Probability Theory Shown by Simulation
Resampling Methods
Applications of Resampling Methods and Monte Carlo Tests
The EM Algorithm
Simulation with Complex Data
System Dynamics and Agent-Based Models
Index

## The EM algorithm by example of k-means clustering

Probably the most famous algorithm for clustering observations to groups is the k-means algorithm. We will see that this algorithm is just a variant of the EM algorithm.

Given n objects, characterized by p variables, we like to partition them into clusters such that cluster has members and each observation is in one cluster. The mean vector (center, prototype), Vk, of a cluster is defined as the centroid of the cluster and the components of the mean vector can be calculated by where is the number of observations in cluster and is the i-th observation belonging to cluster . For each cluster the corresponding cluster means are calculated.

We also need to determine the number of clusters in the output partition. Starting from the given initial locations of the cluster centroids, the algorithm uses the data points to iteratively relocate the centroids and reallocate points to the closest centroid. The process is composed of these steps...