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

Sampling from a chi-squared distribution

Chi-squared distribution is often used by chi-squared tests to inspect the difference between observed value and expected value, or to examine the independence of two variables. In addition, one can infer confidence intervals using chi-squared distribution. In the following recipe, we will discuss how to use R to generate chi-squared distribution further.

In this recipe, you need to prepare your environment with R installed.

How to do it…

Please perform the following steps to generate samples from chi-squared distribution:

1. First, we can use `rchisq` to generate three samples with a degree of freedom equal to `10`:

```> set.seed(123)
> rchisq(3,df=10)
[1]  6.779170 14.757915  3.259122
```
2. We can then use `dchisq` to obtain the density at x=3 with a degree of freedom equal to `10`:

```> dchisq(3,df=10)
[1] 0.02353326
```
3. Also, we can use `pchisq` and `qchisq` to obtain the distribution function and quantile function of the distribution:

`> pchisq(3,df=10...`