Chapter 2 A Gentle Introduction to R
R is a powerful statistical programming language. However, as we’ve seen, when we start R itself, only a command-line window appears. Even when we use RStudio, point-and-click options for statistical analysis aren’t available in the menus. It’s not surprising that new users can be intimidated and confused when they first work with R.
In this section, we’ll start working with R. I’ll focus on simple but useful tasks one might typically do in R. Rather than trying to teach you all of R up front – and hoping you remember it when we get to a topic towards the end of the course – I’ll introduce R functions as they become relevant to the topics we’re studying.
2.1 R as a Calculator
R is always open on my computer desktop. In part, that’s because I use R for even the most basic calculations – literally, as a simple calculator.
Arithmetic is easy is in R and steps for doing so will likely feel natural for you. For example, we can add two numbers
[1] 4We can subtract one number from another
[1] 1We can multiply
[1] 30And we can divide one number by another
[1] 8Exponents are easily handled as well. For example, to calculate \(3^2 = 3*3\) we would type
[1] 9To calculate \(4^3 = 4*4*4\)
[1] 64Interactive Example
Take a second to look over the examples generated below. If you’d like to see another example, click “Show Another.” Prove to yourself that you understand the calculations and can do them yourself. In R/RStudio, enter the same or similar expressions as below and hit Return.
R is also a powerful scientific calculator. In fact, there are too many functions for us to review here. However, we’ll see some functions again and again throughout this class. For example, we’ll often want to calculate the square root of a number \(\sqrt{x}\)
[1] 2.828Euler’s number \(e = 2.7182818284...\) frequently appears in statistics, as does raising \(e\) to a power: \(e^x\). In R, we calculate \(e^x\) using the exp() function. Here, we’ll calculate \(e^3 = \exp(3)\)
[1] 20.09To calculate a logarithm base \(b\) of \(x\), we use the log() command
[1] 3[1] 2.096If we don’t provide log() with a base argument, it defaults to base \(e\) — i.e., a natural logarithm.
[1] 2.303[1] 1The fact that log() defaults to base \(e\) can be confusing. Typically, we would write \(\ln x\) for the logarithm base \(e\) of \(x\) and \(\log_{10} x\) as the logarithm base 10 of \(x\). In R, log(x) calculates the natural log of \(x\), unless we provide a different base \(b\).
Lastly, we can calculate \(x!\) in R using the factorial() function.
[1] 1202.2 Assigning Values to Variables
One of the most important aspects of a programming language is the ability to assign values or calculated results to a variable name. We can think of the variable name as a storage bin for the value. R allows for different types of assignment under different conditions (more on this shortly). However, the most common assignment operator is the backward arrow <-, which is composed of a less than sign < and the dash -.
For example, suppose we want to assign the number 2 to the variable x:
Notice that that R didn’t produce any output as part of the assignment. Instead, look at the Environment tab in the right-side pane. You should now see the variable (or object) x exists in the current working environment and it has a value of 2.
At this point, we can access the value in x simply by referring to the variable name. If we want to display the contents of x, we simply type x at the console and hit Return
[1] 2We can use x in other calculations
[1] 3Here, R substitutes the value held in x (2) into the above expression and then adds 1 to it.
We can do this for multiple variables
Let’s examine the values of y and z
[1] 5[1] 6We calculate expressions that are composed of the variables themselves
[1] -2and we can assign those calculations to a variable name
[1] -2Interactive Example
This example demonstrates assignment to variable names and simple calculation using variable names. Click “Show Another” to generate additional examples. Using the R/RStudio console, prove to yourself that you understand how to perform the assignments and calculations by typing in similar expressions.