First Steps in R

Taking your first steps in R with simple arithmetic operations.

Before you start: the RStudio panes.
Setup: Use R and RStudio. Create or open a project and save first-steps.R as shown below.
Your check: Save, close, reopen and rerun your first R script after restarting R. Practise in the unit summary.

Save and rerun your first script

A script keeps your commands in a file so you can inspect, change and run them again. We will keep scripts and, later, data together in an RStudio project. If you already have a course project, open its .Rproj file and use that folder for this practice.

1. In RStudio, choose File > New Project > New Directory > New Project. Name the directory base-r-practice, choose a location you can find again, and click Create Project. RStudio creates the folder and a file named base-r-practice.Rproj inside it.
2. Choose File > New File > R Script. A blank tab opens in the script editor. Enter the code below, including the comment.
3. Choose File > Save As and save the file as first-steps.R inside your project folder, beside the .Rproj file. The .R extension identifies an R script.

# My first saved R script
hello <- "Welcome to R"
hello
1 + 2

Select all four lines in the script editor and click Run, or press Ctrl+Enter on Windows/Linux or Cmd+Enter on macOS. R runs them in order. The Console displays "Welcome to R" and 3; hello also appears in the Environment pane. The next section explains the comment and assignment arrow.

Check that the file is enough: save it, close its editor tab, then use File > Open File to reopen first-steps.R. Choose Session > Restart R, select all its lines and run them again. You should get the same results. Reopening a script displays the saved code; running it recreates its objects.

For this practice, use Tools > Project Options > General to turn off restoring .RData at startup and set saving the workspace on exit to Never. Continue saving your .R files. This makes the script the record of your work, without relying on objects left over from an earlier session. Next time, open the .Rproj first, then your script.

#Hashtag and Run!

Outside quoted text, # starts a comment in R. The text after it on the same line is not executed. Use comments to explain your code to yourself and others.

# This is a comment. Comments are very helpful
# when you want to describe what's going on in your code.
# Use them often!

hello <- "Welcome to R" #the variable "hello" is storing the information "Welcome to R"

Text such as This is not a comment anymore. without a leading # or quotation marks is not valid R code. Running it produces a syntax error. To keep a note in your script, add # at the start of the line; to store text as a value, put it in quotation marks as in hello above.

To run a line in an R script, place the cursor on that line and click the “Run” button in the script editor (red box in the following picture). Alternatively, press CTRL + ENTER on Windows/Linux or CMD + ENTER on a Mac. Select several lines first to run them together.

Hit the Run-Button.

RStudio sends the selected code to the Console, where you see the commands and their output. The following is a console transcript, not a block to paste into a script. The > symbols are prompts supplied by R:

> hello <- "Welcome to R"
> hello
[1] "Welcome to R"
>

Here, you’ll also see on the left hand side the “>” symbol which means that R is ready to receive a new command. If a “+” is visible instead, this means that the command has not yet been completed, e.g. a parenthesis has not been closed.

If the Console keeps showing +, press Esc to cancel the unfinished command, then check the complete line in your script for a missing quote or closing parenthesis. If you see object 'hello' not found, run the line creating hello before displaying it. Correct the saved script and rerun its lines from the top.

Creating scalar objects and simple arithmetic operations

The basic arithmetic operations are addition, subtraction, multiplication and division. Further, more complex operations include square roots, exponentiation and other operations. To control the order of operations, use parentheses “()”. Note that square brackets “[]” cannot be used, because they are reserved for subsetting or indexing data structures like vectors, lists, data frames, and matrices, as you will see in Unit 04.

Examples of mathematical operations in R. This is using R like a calculator.

Operator	Description	Example
Arithmetic Operators
+	Addition	x + y
-	Subtraction	x - y
*	Multiplication	x * y
/	Division	x / y
^ or **	Exponentiation	x^y
x %% y	Modulus (x mod y)	x %% y
%/%	Integer division	x %/% y
Math Functions
log()	Logarithms, by default natural	log(x)
exp()	Exponential function	exp(x)
sqrt()	Square-root	sqrt(x)
^(1/n)	nth roots	x^(1/n)
abs()	Absolute value	abs(x)
sin()	Sine	sin(x)
cos()	cosine	cos(x)
tan()	Tangent	tan(x)

Run these commands separately. Each R code block is followed by its console output:

1 + 2

[1] 3

2 - 1

[1] 1

2 * 3

[1] 6

2 / 3

[1] 0.6666667

2 ^ 3

[1] 8

cos(2 ^ (3 + 2))

[1] 0.8342234

R code uses a decimal point. The number of digits printed depends on the display settings; the stored result is more precise than this default output.

That [1] next to your result is a reminder that this line begins with the first value in your result. Some commands return more than one value, and their results may fill up multiple lines.

Assigning values to objects

Assignment gives a name to a value so you can use it again. Write the object name, the assignment arrow <-, and the expression whose result you want to store. R also permits = for some assignments; this course uses <-. In the next lesson, you will see how = supplies a named argument inside a function call, while == tests equality.

# Store the result of the addition in a, then display it
a <- 1 + 2
a

[1] 3

# Store another result
b <- 2 - 1
b

[1] 1

a + b

[1] 4

c <- (a + b) * 2
c

[1] 8

Assignment stores a result under a name. Typing that name, or calling print(a), displays the stored value.

Ready to continue: your reopened script recreates its results after restarting R. Continue with R Syntax to read a function call and import a small supplied file.