#### Overview of this book

This cookbook offers a range of data analysis samples in simple and straightforward R code, providing step-by-step resources and time-saving methods to help you solve data problems efficiently. The first section deals with how to create R functions to avoid the unnecessary duplication of code. You will learn how to prepare, process, and perform sophisticated ETL for heterogeneous data sources with R packages. An example of data manipulation is provided, illustrating how to use the “dplyr” and “data.table” packages to efficiently process larger data structures. We also focus on “ggplot2” and show you how to create advanced figures for data exploration. In addition, you will learn how to build an interactive report using the “ggvis” package. Later chapters offer insight into time series analysis on financial data, while there is detailed information on the hot topic of machine learning, including data classification, regression, clustering, association rule mining, and dimension reduction. By the end of this book, you will understand how to resolve issues and will be able to comfortably offer solutions to problems encountered while performing data analysis.
R for Data Science Cookbook
Credits
www.PacktPub.com
Preface
Free Chapter
Functions in R
Data Preprocessing and Preparation
Visualizing Data with ggplot2
Making Interactive Reports
Simulation from Probability Distributions
Statistical Inference in R
Time Series Mining with R
Index

## Determining the number of principal components using a scree plot

As we only need to retain the principal components that account for most of the variance of the original features, we can either use the Kaiser method, a scree plot, or the percentage of variation explained as the selection criteria. The main purpose of a scree plot is to graph the component analysis results as a scree plot and find where the obvious change in slope (elbow) occurs. In this recipe, we will demonstrate how to determine the number of principal components using a scree plot.

Ensure you have completed the previous recipe by generating a principal component object and saving it in variable `eco.pca`.

### How to do it…

Perform the following steps to determine the number of principal components with a scree plot:

1. First, generate a bar plot by using `screeplot`:

``` > screeplot(swiss.pca, type="barplot")
```

Figure 16: The scree plot in bar plot form

2. You can also generate a line plot by using `screeplot`:

`> screeplot...`