When we work with R, we often do this using a command line in which we type commands and it responds to those commands. In the simplest case, if we just type in a number, it will simply respond with that number. Go into the R console and type the number 3. You should see somethign like this:
> 3  3
> symbol is the command prompt, which is prompting you to type something in. The next line (
 3) is R’s answer. Let’s try something a bit more complicated:
> 3 + 4  7
R spits out the answer to whatever you type in, as long as it can figure it out. Now let’s try typing in a word:
> hello Error: object 'hello' not found
What? Why did this happen? When R encounters a letter or word, it assumes that it is referring to the name of a variable — think of
X from high school algebra. We will return to variables in a little while, but if we want R to print out the word hello then we need to contain it in quotation marks, telling R that it is a character string.
> "hello"  "hello"
There are many types of variables in R. You have already seen two examples: integers (like the number 3) and character strings (like the word “hello”). Another important one is real numbers, which are the most common kind of numbers that we will deal with in statistics, which span the entire number line including the spaces in between the integers. For example:
> 1/3  0.33
In reality the result should be 0.33 followed by an infinite number of threes, but R only shows us two decimal points in this example.
Another kind of variable is known as a logical variable, because it is based on the idea from logic that a statement can be either true or false. In R, these are capitalized (
To determine whether a statement is true or not, we use logical operators. You are already familiar with some of these, like the greater-than (
>) and less-than (
> 1 < 3  TRUE > 2 > 4  FALSE
Often we want to know whether two numbers are equal or not equal to one another. There are special operators in R to do this:
== for equals, and
!= for not-equals:
> 3 == 3  TRUE > 4 != 4  FALSE