1 Getting started

(AST230) R for Data Science

Author

Md Rasel Biswas

Getting Started with R

  • When you type something into the console, R will give you a reply. For example:
2+4
[1] 6
  • As you probably expected, R returned 6.
Note:
  • You can ignore the [1] you see in the returned value. That’s just R saying that 6 is the 1st value (and only value here) of the output line.
  • R can be used as a calculator.
(59 + 73 + 2) / 3
[1] 44.66667
10^(3+1)
[1] 10000
Note:
  • Arithmetic operators are the same as they are in most other computer applications.

Arithmetic operators

Description Operator
Addition +
Subtraction -
Multiplication *
Division /
Exponentiation ^ or **
integer division 10%/%3 is 3 x %/% y
modulus (x mod y) 10%%3 is 1 x %% y

Exercise 1.1

Use R to calculate the following:

  • 5^2
  • Add 8 to 22 and then multiply the answer by 3
  • Divide 8 by 2.5 and then divide the answer by 3
Notice

The above calculations do not produce any kind of output that is remembered by R

Creating objects

  • To store our calculations in R we need to give it a name and tell R to store that as an object.

  • Assignment operators <- or = can be used to assign a value to an R object, and it is preferable to use <- as = has other uses.

my_obj <- 48

  • Now that we’ve created this object, R knows all about it and will keep track of it during this current R session

  • All of the objects you create will be stored in the current workspace and you can view all the objects in your workspace in RStudio by clicking on the Environment tab in the top right-top pane

  • If you click on the down arrow on the ‘List’ icon in the same pane and change to ‘Grid’ view, RStudio will show you a summary of the objects including
    • the type (numeric - it’s a number)
    • the length (only one value in this object)
    • its ‘physical’ size, and
    • its value (48 in this case)
  • There are many different types of values that you can assign to an object. For example
my_obj2 <- "R is cool"
  • Here we have created an object called my_obj2 and assigned it a value of R is cool which is a character string.
Note
  • We have enclosed the string in quotes.
  • If you forget to use the quotes you will receive an error message.
my_obj2 <- R is cool
Error in parse(text = input): <text>:1:14: unexpected symbol
1: my_obj2 <- R is
                 ^
  • Our workspace now contains both objects we’ve created so far with my_obj2 listed as type character.

  • To change the value of an existing object we simply reassign a new value to it.

  • For example, to change the value of my_obj2 from "R is cool" to the number 1024

my_obj2 <- 1024

  • Once we have created a few objects, we can do stuff with our objects.

  • For example, the following code creates a new object my_obj3 and assigns it the value of my_obj added to my_obj2 which is 1072 (48 + 1024 = 1072)

my_obj3 <- my_obj + my_obj2
my_obj3
[1] 1072
char_obj <- "hello"
char_obj2 <- "world!"
char_obj3 <- char_obj + char_obj2
Error in char_obj + char_obj2: non-numeric argument to binary operator

  • Reading the error message is important in R

  • This error message is essentially telling you that either one or both of the objects char_obj and char_obj2 is not a number and therefore cannot be added together

  • Another error message that you’ll get quite a lot when you first start using R is Error: object '**' not found. As an example, take a look at the code below.
my_obj <- 48
my_obj4 <- my_obj + no_obj
Error: object 'no_obj' not found

  • R returns an error message because we haven’t created (defined) the object no_obj yet.

  • If you check your environment, you’ll see that object my_obj4 has not been created

Naming objects

  • In R, object names are case sensitive, and a valid object name (syntactic name) consists of a combination of

    • (a-z, A-Z), (0-9), (.), (-), and (_)

    • An object name cannot start with a number or a hyphen or an underscore and can start with a dot, but it must be followed by a letter

  • A good programming practice is to use meaningful object names in the codes, and self-explanatory object names increase the readability of the codes

  • Existing R functions, names, or words (e.g., mean, log, exp, TRUE, c, etc.) should not be used as object names

Exercise 1.2

  1. Create an object called x1 which is the number 73
  2. Create another object called x2 which is the answer to the sum 101+36
  3. Multiply x1 and x2 together and store the object as another object called x3
  4. Subtract 1 from x3 and calculate the 4th root.
  5. The answer should be 10

Use of brackets

  • Parentheses ( & ) are used to define arithmetic expressions, and they must be matched; unmatched parentheses will result in errors
((3 + 12)/3 + 8)
[1] 13
  • Using curly brackets { & } do not result in any error but should not be used as they have some specific uses in R, e.g. defining a function
{10 + 2}+ 5
[1] 17
  • The square brackets [ & ] cannot be used in arithmetic expressions
[2 + 7]/3
Error in parse(text = input): <text>:1:1: unexpected '['
1: [
    ^

R functions

  • Functions are ready-made pieces of codes.
  • Some of the mathematical functions in R:
Description R symbol Example
square root sqrt sqrt(225)
natural logarithm log log(50)
exponential exp exp(3)
absolute abs abs(-10)
factorial factorial factorial(6)
sine function sin sin(25)
inverse cosine acos acos(-8.67)
  • R has a large collection of built-in functions that are called like this:
function_name(arg1 = val1, arg2 = val2, ...)

  • Let’s try using sqrt()

    • sqrt(25) or sqrt(x = 25) will return a value 5
Note
  • inputs (called arguments in R) should be within the parentheses ( ) even if there’s no input.
  • Multiple inputs, if needed, are separated by commas, e.g. fun_name(input1, input2, input3)

Some useful built-in R functions

round(3.567, digits=2)
[1] 3.57
floor(3.567)
[1] 3
ceiling(3.567)
[1] 4
pi   # Not a function, but useful
[1] 3.141593

R ignores excess spacing

(1+2)     ^     3
[1] 27
    ( 1+  2)    ^ 3
[1] 27

  • Basically, you can put spaces between different values, and you can put as many as you want and R won’t care.

  • However, if you insert a space within a single value, R will generate an error.

3   .14
Error in parse(text = input): <text>:1:5: unexpected numeric constant
1: 3   .14
        ^

Commenting codes

R will ignore anything on the same line that follows the # symbol.

# Calculating BMI
weight <- 70 # This is in kg
height <- 1.7 # This is in meter
bmi <- weight / height ^ 2
bmi
[1] 24.22145

Exercise 1.3

  1. Why does this code not work?
my_variable <- 10
my_varıable
Error: object 'my_varıable' not found

Exercise 1.4

  1. Create an object called myObject and assign it a value between 1 and 100

  2. Add 13 to myObject, making sure the object itself stores the updated value

  3. Is myObject divisible by 2? by 3? by 13? by 21? Use the R code to get the answer.

  4. How many times can 5 fit in myObject?