Hands-On Programming with R

Chapter 6. Environments

Your deck is now ready for a game of blackjack (or hearts or war), but are your shuffle and deal functions up to snuff? Definitely not. For example, deal deals the same card over and over again:

deal(deck)
## face   suit value
## king spades    13

deal(deck)
## face   suit value
## king spades    13

deal(deck)
## face   suit value
## king spades    13

And the shuffle function doesn’t actually shuffle deck (it returns a copy of deck that has been shuffled). In short, both of these functions use deck, but neither manipulates deck—and we would like them to.

To fix these functions, you will need to learn how R stores, looks up, and manipulates objects like deck. R does all of these things with the help of an environment system.

Environments

Consider for a moment how your computer stores files. Every file is saved in a folder, and each folder is saved in another folder, which forms a hierarchical file system. If your computer wants to open up a file, it must first look up the file in this file system.

You can see your file system by opening a finder window. For example, Figure 6-1 shows part of the file system on my computer. I have tons of folders. Inside one of them is a subfolder named Documents, inside of that subfolder is a sub-subfolder named ggsubplot, inside of that folder is a folder named inst, inside of that is a folder named doc, and inside of that is a file named manual.pdf.

Figure 6-1. Your computer arranges files into a hierarchy of folders and subfolders. ...