Tag Archives: statistics

Making and Using Variables in R

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Variables are used in R to store information for computational purposes. It seems that there is almost no limit to what can be stored in a variable. To make a variable, you need to know the following information.

  • The name you want to give the variable
  • The information you want to store in the variable

Here is an example,

You want to make a variable that will store the following test score: 80, 81, 82, 83, 84, 85. You want to call the variable test_scores. Here is what we know

  • The name of the variable is test_scores
  • It will contain the values of 80, 85, 90, 95, 100

Here is how this would look in R.

  • > test_score <- 80:85

There are a few things to explain

  1. the <- sign means “assigned to” in other words, the variable name on the left of the <- sign is being assigned to the values 80:85.
  2. The colon sign stands for a sequence. We wanted all whole numbers from 80 to 85 and the colon sign provides this information.
  3. Both the <- and : are known as operators in R. Operators symbols you place between numbers in order to make a calculation.

Know, type test_scores into the R console and press enter. You should see the following.

  • > test_scores
[1] 80 81 82 83 84 85

R now shows you everything that is stored in the variable. We can also created other variables and perform calculations through the use of variables. For example, let’s say that you want to add 5 points of extra credit to the scores of the test. To do this let’s make a variable called extra_credit and add test_scores to extra_credit

  • > extra_credit <- 5
> test_scores + extra_credit
[1] 85 86 87 88 89 90

As you can see, R took the values of test_scores and add extra_credit to each value in test_scores.  This is much faster than entering each value separately to calculate it. We can also make a new variable for the new scores and we can call it revised_test_scores Let’s try

  • > revised_test_scores <- test_scores + extra_credit
> revised_test_scores
[1] 85 86 87 88 89 90

Variables can also be used for text. The only difference is that you must put quotes around the words. Otherwise, the computer will think the words are numbers, which does not make sense. Below is an example,

  • > h <- "Howdy"
> h
[1] "Howdy"

Lastly, variables can be used to store vectors. This is very useful in saving a lot of time in performing calculations. We will now  make the variable student_names and assigned a vector to it containing the names of students.

  • > student_names <- c("David", "Edward", "John")
> student_names
[1] "David" Edward" "John"

This is only the beginning of some of the amazing features of R.

Introduction to Vectors in R

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A key component of R is the use of vectors. Vectors a single piece of information that contents a collection of information. This probably sounds extremely confusing so an example will be provided.

Think of an organization such as a school. We will call the school Asia International School. Asia International school consist of an administrator named Dr. T, teachers named Mr. Bob and Mrs . Smith, and students named Sam, David, and Mary. In this example, the school is consider a vector or a single piece of information (Asia International School). The administrators, teachers, and students are the collection of information within the large piece of information that is the school.

If we wanted to write this example using the R programming language it would look something like the following…

  • > Asia International School(Dr. T, Mr. Bob, Mrs. Smith, Sam, David, Mary)
[1] Dr. T Mr. Bob Mrs. Smith Sam David Mary

To be fair this is not exactly how it is done this is strictly an imperfect illustration of a very abstract concept.

A Real Example

In order to make a vector in R you need to use c() function. A function is a piece of code that does something to the information that is within its parentheses. For example, let’s make a vector that contains the numbers 1, 2, 3, 4, 5.

  • > c(1,2,3,4,5)
[1] 1 2 3 4 5

To get the second line you need you press enter

The c means combine. The information inside the parentheses is the information that is being combined into one vector. Going back to our school example, Dr. T, Mr. Bob, Mrs. Smith, Sam, David, and Mary were being combined into the school Asia International. In a vector, all information inside the parentheses is known as arguments.

Conclusion

This is just some of the most basic ideas about vectors. There is a great deal more to explore about the use of vectors which is considered one of the most powerful features of R. The challenge of learning R is with the abstract nature of programming. You have to think of things you want to do in terms of a code that the computer can understand. This is very confusing for most people.