In this book, you will find a number of styles of text that distinguish between different kinds of information. Here are some examples of these styles and an explanation of their meaning.

Code words in text, folder names, filenames, file extensions, and pathnames are shown as follows: "Here, we created a data.frame object named df by combining the vectors num, lower, and upper."

A block of code is set as follows:

> num = 1:4
> lower = c("a","b","c","d")
> upper = c("A","B","C","D")
> df = data.frame(num, lower, upper)
> df
  num lower upper
1   1     a     A
2   2     b     B
3   3     c     C
4   4     d     D

New terms and important words are shown in bold. Words that you see on the screen, in menus or dialog boxes for example, appear in the text like this: "Under the Getting Started section, select the download R link."