80 + 20 + 527 + 15 + 1700 + 854 First Contact with R
If you are new to R and don’t have any programming experience, then you should read this chapter in its entirety. If you already have some previous experience working with R and/or have some programming background, then you may want to skim over most of the introductory chapters of part I.
This chapter, and the rest of the book, assumes that you have installed both R and RStudio in your computer. If this is not the case, then go to chapters Installing R and Installing RStudio to follow the steps for downloading and installing these programs.
R comes with a simple built-in graphical user interface (GUI), and you can certainly start working with it right out of the box. That is actually the way I got my first contact with R back in 2001 during my senior year in college. Nowadays, instead of using R’s GUI, it is more convenient to interact with R using a third party software such as RStudio.
I describe more introductory details about RStudio in the chapter A Quick Tour Around RStudio. For now, go ahead and launch RStudio in your computer.
4.1 First Contact with R (via RStudio)
When you open RStudio, you should be able to see its layout organized into quadrants officially called panes. The very first time you launch RStudio you will only see three panes, like in the screenshot below.
4.2 Interacting with R’s Console
To help you break the ice with R, it’s better if we start working directly on the Console.
As you can tell from the following screenshot, the console is located in the left-hand side quadrant of RStudio. Keep in mind that your RStudio’s console pane may be located in a different quadrant.
Technically speaking, the console is a terminal where a user inputs commands and views output. Simply put, this is where you can directly interact with R by typing commands, and getting the output from the execution of the commands.
4.2.1 R as a scientific calculator
This first activity is dedicated for readers with little or no programming experience, especially those of you who have never used software in which you have to type commands. The idea is to start typing simple things in the console, basically using R as a scientific calculator.
Here’s a toy example. Consider the monthly bills of an undergraduate student:
- cell phone $80
- transportation $20
- groceries $527
- gym $15
- rent $1700
- other $85
You can use R to find the student’s total expenses by typing these commands in the console:
There is nothing surprising or fancy about this piece of code. In fact, it has all the numbers and all the + symbols that you would use if you had to obtain the total expenses by using the calculator in your cellphone.
4.2.2 Assigning values to objects
Often, it will be more convenient to create objects, sometimes also called variables, that store one or more values. To do this, type the name of the object, followed by the assignment or “arrow” operator <-, followed by the assigned value. By the way, the arrow operator consists of a left-angle bracket < (or “less than” symbol) and a dash or hyphen symbol -.
For example, you can create an object phone to store the value of the monthly cell phone bill, and then inspect the object by typing its name:
phone <- 80
phone[1] 80All R statements where you create objects are known as assignments, and they have this form:
object <- valuethis means you assign a value to a given object; one easy way to read the previous assignment is “phone gets 80”.
Alternatively, you can also use the equals sign = for assignments:
transportation = 20
transportation[1] 20As you will see in the rest of the book, I’ve written most assignments with the arrow operator <-. But you can perfectly replace them with the equals sign =. The opposite is not necessarily true. There are some especial cases in which an equals sign cannot be replaced with the arrow, but we’ll talk about this later.
Pro tip. RStudio has a keyboard shortcut for the arrow operator<-:
Windows & Linux users:
Alt+-Mac users:
Option+-
In fact, there is a large set of keyboard shortcuts. In the menu bar, go to the Help tab, and then click on the option Keyboard Shorcuts Help to find information about all the available shortcuts.
4.2.3 Object Names
There are certain rules you have to follow when creating objects and variables. Object names cannot start with a digit and cannot contain certain other characters such as a comma or a space.
The following are invalid names (and invalid assignments)
# cannot start with a number
5variable <- 5
# cannot start with an underscore
_invalid <- 10
# cannot contain comma
my,variable <- 3
# cannot contain spaces
my variable <- 1People use different naming styles, and at some point you should also adopt a convention for naming things. Some of the common styles are:
snake_case
camelCase
period.casePretty much all the objects and variables that I create in this book follow the “snake_case” style. It is certainly possible that you may end up working with a team that has a style-guide with a specific naming convention. Feel free to try various styles, and once you feel comfortable with one of them, then stick to it.
4.2.4 Case Sensitive
R is case sensitive. This means that phone is not the same as Phone or PHONE
# case sensitive
phone <- 80
Phone <- -80
PHONE <- 8000
phone + Phone[1] 0PHONE - phone[1] 7920Again, this is one more reason why adopting a naming convention early on in a data analysis or programming project is very important. Being consistent with your notation may save you from some headaches down the road.
4.2.5 Calling Functions
Like any other programming language, R has many functions. To use a function just type its name followed by parenthesis. Inside the parenthesis you typically pass one or more inputs. Most functions will produce some type of output:
# absolute value
abs(10)
abs(-4)
# square root
sqrt(9)
# natural logarithm
log(2)In the above examples, the functions are taking a single input. But often you will be working with functions that accept several inputs. The log() function is one them. By default, log() computes the natural logarithm. But it also has the base argument that allows you to specify the base of the logarithm, say to base = 10
log(10, base = 10)[1] 14.3 Exercises
1) Here’s the list of monthly expenses for a hypothetical undergraduate student
- cell phone $80
- transportation $20
- groceries $550
- gym $15
- rent $1700
- other $85
- Using the
consolepane of RStudio, create objects (i.e. variables) for each of these expenses listed above, and then create an objecttotalwith the sum of the expenses.
Show answer
cellphone = 80
transportation = 20
groceries = 550
gym = 15
rent = 1700
other = 85
total = cellphone + transportation + groceries + gym + rent + other- Assuming that the student has the same expenses every month, how much would she spend during a school “semester”? (assume the semester involves five months). Write code in R to find this value.
Show answer
semester_exps = total * 5- Using the same assumption about the monthly expenses, how much would she spend during a school “year”? (assume the academic year is 10 months). Write code in R to find this value.
Show answer
year_exps = total * 102) Write code in the console to calculate: \(3x^2 + 4x + 8\) when \(x = 2\)
Show answer
x = 2
(3 * x^2) + (4 * x) + 83) Calculate: \(3x^2 + 4x + 8\) but now with a numeric sequence for \(x\) using x <- -3:3
Show answer
x = -3:3
(3 * x^2) + (4 * x) + 8
4.2.6 Comments in R
All programming languages use a set of characters to indicate that a specifc part or lines of code are comments, that is, things that are not to be executed. R uses the hash or pound symbol
#to specify comments. Any code to the right of#will not be executed by R.You will notice that I have included comments in almost all of the code snippets shown in the book. To be honest, some examples may have too many comments, but I’ve done that to be very explicit, and so that those of you who lack coding experience understand what’s going on. In real life, programmers use comments, but not so much as I do in the book. The main purpose of writing comments is to describe—conceptually—what is happening with certain lines of code. Some would even argue that comments should only be used to express not the what but the why a developer is doing something. In case of doubt, especially if you don’t have a lot of programming experience, I think it’s better to err on the side of caution by adding more comments than including no comments whatsoever.