Today's lab introduces the R programming language.

Getting Started with R

Before we start writing R code on our machines, we're going to start with a fun tutorial that demonstrate some of the syntatic differences between Python and R.

Using R on the Lab Computers

The R programming language is freely available (see below for downloading on your own computer). On the lab machines, R has been downloaded and is in the Applications folder. To find it, navigate to Applications or use Spotlight (the built-in search function-- the magnifying glass icon on the right side of the top menu bar) and type R.

(Note: R can also be launched from the terminal window by typing: R.)

When launched, a window will pop up labeled R Console. This functions much in the same way as the Python Shell. Let's start by saying hello to the world. At the console prompt (the > line at the bottom of the window), type: 

	print("Hello World!")
The message, Hello World! will be printed below the command, just as it did in the Python shell.

Let's try the same command but stretched out over multiple lines: 

	print("Hello
When you hit enter, the prompt changes from a > to a + to let you know that R thinks that more is needed for the command. Let's finish it with: 
	World")

You can end R commands with a enter/return (as in Python), or with a semi-colon (;).

As in Python, we can have comments: 

	#This is a comment

As in Python, anything after the # is information for the user and is ignored as a command.

We now have all the pieces to write our first R program!

  1. On the menu bar of the R Console, click the plain-piece-of-paper icon (second from the right):

    This will be open up a new window where you can write an R program.

  2. In your new window, type: 
    	#My first R program
	#My name
	#April 19, 2017

	print("Hello World")
  3. Save your file, using the File menu.
  4. To run your program, go back to the R Console and click on the R icon (second from the left):

    You will see a prompt for which file you would like to run. Choose the one you just saved. The output will appear in the console window.

  5. When you are done with R, you can quit the console by using the menu or typing q().

For Loops in R

For-loops are very similar in R to those in Python. The basic format is: 

for (var in seq) expr

where

Let's use a simple way to create a vector of numbers: 

	1:10
will give 1 2 3 4 5 6 7 8 9 10. The general form is like the range statement in Python: 
	start:stop

But unlike Python, it includes the last number!

If the stop is smaller than the start, R will create a vector with the numbers in reverse order: 

	10:1
will output 10 9 8 7 6 5 4 3 2 1.

Let's use this simple vector of numbers as the sequence for the for loop: 

for (i in 1:5) print(i)

This will print the first 5 numbers.

Challenges

Let's redo some of our early Python programs in R:

In-class Quiz

During lab, there is a paper quiz on Programs 26-30. As with all paper quizzes, no extra materials (notes, book, computer, etc.) are allowed.

What's Next?

If you finish the lab early, now is a great time to get a head start on the programming problems due early next week. There's instructors to help you and you already have Python up and running. The Programming Problem List has problem descriptions, suggested reading, and due dates next to each problem.

Using R at Home

To duplicate the setting in the lab, you will need to download and install: R is also available for Windows and other platforms.