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R Introduction

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What is R

R is a popular programming language used for statistical computing and graphical presentation.

Its most common use is to analyze and visualize data.

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Why Use R?

• It is a great resource for data analysis, data visualization, data science and machine learning
• It provides many statistical techniques (such as statistical tests, classification, clustering and data reduction)
• It is easy to draw graphs in R, like pie charts, histograms, box plot, scatter plot, etc++
• It works on different platforms (Windows, Mac, Linux)
• It is open-source and free
• It has a large community support
• It has many packages (libraries of functions) that can be used to solve different problems

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R Get Started

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How to Install R

To install R, go to https://cloud.r-project.org/ and download the latest version of R for Windows, Mac or Linux.

When you have downloaded and installed R, you can run R on your computer.

The screenshot below shows how it may look like when you run R on a Windows PC:

If you type 5 + 5, and press enter, you will see that R outputs 10.

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Learning R at W3Schools

When learning R at W3Schools.com, you can use our “Try it Yourself” tool, which shows both the code and the result in your browser. This will make it easier for you to test and understand every part as we move forward:

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R Syntax

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Syntax

To output text in R, use single or double quotes:

To output numbers, just type the number (without quotes):

To do simple calculations, add numbers together:

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R Print Output

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Print

Unlike many other programming languages, you can output code in R without using a print function:

However, R does have a print() function available if you want to use it. This might be useful if you are familiar with other programming languages, such as Python, which often uses the print() function to output code.

And there are times you must use the print() function to output code, for example when working with for loops (which you will learn more about in a later chapter):

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R Comments

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Comments can be used to explain R code, and to make it more readable. It can also be used to prevent execution when testing alternative code.

Comments starts with a #. When executing code, R will ignore anything that starts with #.

This example uses a comment before a line of code:

This example uses a comment at the end of a line of code:

Comments does not have to be text to explain the code, it can also be used to prevent R from executing the code:

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Multiline Comments

Unlike other programming languages, such as Java, there are no syntax in R for multiline comments. However, we can just insert a # for each line to create multiline comments:

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R Variables

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Creating Variables in R

Variables are containers for storing data values.

R does not have a command for declaring a variable. A variable is created the moment you first assign a value to it. To assign a value to a variable, use the <- sign. To output (or print) the variable value, just type the variable name:

From the example above, name and age are variables, while "John" and 40 are values.

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Print / Output Variables

Compared to many other programming languages, you do not have to use a function to print/output variables in R. You can just type the name of the variable:

However, R does have a print() function available if you want to use it. This might be useful if you are familiar with other programming languages, such as Python, which often use a print() function to output variables.

And there are times you must use the print() function to output code, for example when working with for loops (which you will learn more about in a later chapter):

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Concatenate Elements

You can also concatenate, or join, two or more elements, by using the paste() function.

To combine both text and a variable, R uses comma (,):

You can also use , to add a variable to another variable:

For numbers, the + character works as a mathematical operator:

If you try to combine a string (text) and a number, R will give you an error:

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Multiple Variables

R allows you to assign the same value to multiple variables in one line:

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Variable Names

A variable can have a short name (like x and y) or a more descriptive name (age, carname, total_volume). Rules for R variables are:

• A variable name must start with a letter and can be a combination of letters, digits, period(.)
  and underscore(_). If it starts with period(.), it cannot be followed by a digit.
• A variable name cannot start with a number or underscore (_)
• Variable names are case-sensitive (age, Age and AGE are three different variables)
• Reserved words cannot be used as variables (TRUE, FALSE, NULL, if…)

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R Data Types

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In programming, data type is an important concept.

Variables can store data of different types, and different types can do different things.

In R, variables do not need to be declared with any particular type, and can even change type after they have been set:

R has a variety of data types and object classes. You will learn much more about these as you continue to get to know R.

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Basic Data Types

Basic data types in R can be divided into the following types:

• numeric – (10.5, 55, 787)
• integer – (1L, 55L, 100L, where the letter “L” declares this as an integer)
• complex – (9 + 3i, where “i” is the imaginary part)
• character (a.k.a. string) – (“k”, “R is exciting”, “FALSE”, “11.5”)
• logical (a.k.a. boolean) – (TRUE or FALSE)

We can use the class() function to check the data type of a variable:

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R Numbers

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There are three number types in R:

• numeric
• integer
• complex

Variables of number types are created when you assign a value to them:

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Numeric

A numeric data type is the most common type in R, and contains any number with or without a decimal, like: 10.5, 55, 787:

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Integer

Integers are numeric data without decimals. This is used when you are certain that you will never create a variable that should contain decimals. To create an integer variable, you must use the letter L after the integer value:

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Complex

A complex number is written with an “i” as the imaginary part:

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Type Conversion

You can convert from one type to another with the following functions:

• as.numeric()
• as.integer()
• as.complex()

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R Math

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Simple Math

In R, you can use operators to perform common mathematical operations on numbers.

The + operator is used to add together two values:

And the - operator is used for subtraction:

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Built-in Math Functions

R also has many built-in math functions that allows you to perform mathematical tasks on numbers.

For example, the min() and max() functions can be used to find the lowest or highest number in a set:

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sqrt()

The sqrt() function returns the square root of a number:

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abs()

The abs() function returns the absolute (positive) value of a number:

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ceiling() and floor()

The ceiling() function rounds a number upwards to its nearest integer, and the floor() function rounds a number downwards to its nearest integer, and returns the result:

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R Strings

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Strings are used for storing text.

A string is surrounded by either single quotation marks, or double quotation marks:

"hello" is the same as 'hello':

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Assign a String to a Variable

Assigning a string to a variable is done with the variable followed by the <- operator and the string:

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Multiline Strings

You can assign a multiline string to a variable like this:

However, note that R will add a “\n” at the end of each line break. This is called an escape character, and the n character indicates a new line.

If you want the line breaks to be inserted at the same position as in the code, use the cat() function:

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String Length

There are many usesful string functions in R.

For example, to find the number of characters in a string, use the nchar() function:

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Check a String

Use the grepl() function to check if a character or a sequence of characters are present in a string:

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Combine Two Strings

Use the paste() function to merge/concatenate two strings:

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Escape Characters

To insert characters that are illegal in a string, you must use an escape character.

An escape character is a backslash \ followed by the character you want to insert.

An example of an illegal character is a double quote inside a string that is surrounded by double quotes:

To fix this problem, use the escape character \":

Other escape characters in R:

Code	Result
\\	Backslash
\n	New Line
\r	Carriage Return
\t	Tab
\b	Backspace

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R Booleans / Logical Values

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Booleans (Logical Values)

In programming, you often need to know if an expression is true or false.

You can evaluate any expression in R, and get one of two answers, TRUE or FALSE.

When you compare two values, the expression is evaluated and R returns the logical answer:

You can also compare two variables:

You can also run a condition in an if statement.

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R Operators

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Operators are used to perform operations on variables and values.

In the example below, we use the + operator to add together two values:

R divides the operators in the following groups:

• Arithmetic operators
• Assignment operators
• Comparison operators
• Logical operators
• Miscellaneous operators

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R Arithmetic Operators

Arithmetic operators are used with numeric values to perform common mathematical operations:

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R Assignment Operators

Assignment operators are used to assign values to variables:

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R Comparison Operators

Comparison operators are used to compare two values:

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R Logical Operators

Logical operators are used to combine conditional statements:

Operator	Description
&	Element-wise Logical AND operator. It returns TRUE if both elements are TRUE
&&	Logical AND operator – Returns TRUE if both statements are TRUE
|	Elementwise- Logical OR operator. It returns TRUE if one of the statement is TRUE
||	Logical OR operator. It returns TRUE if one of the statement is TRUE.
!	Logical NOT – returns FALSE if statement is TRUE

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R Miscellaneous Operators

Miscellaneous operators are used to manipulate data:

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R If … Else

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Conditions and If Statements

R supports the usual logical conditions from mathematics:

These conditions can be used in several ways, most commonly in “if statements” and loops.

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The if Statement

An “if statement” is written with the if keyword, and it is used to specify a block of code to be executed if a condition is TRUE:

In this example we use two variables, a and b, which are used as a part of the if statement to test whether b is greater than a. As a is 33, and b is 200, we know that 200 is greater than 33, and so we print to screen that “b is greater than a”.

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Else If

The else if keyword is R’s way of saying “if the previous conditions were not true, then try this condition”:

In this example a is equal to b, so the first condition is not true, but the else if condition is true, so we print to screen that “a and b are equal”.

You can use as many else if statements as you want in R.

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If Else

The else keyword catches anything which isn’t caught by the preceding conditions:

In this example, a is greater than b, so the first condition is not true, also the else if condition is not true, so we go to the else condition and print to screen that “a is greater than b”.

You can also use else without else if:

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Nested If Statements

You can also have if statements inside if statements, this is called nested if statements.

AND

The & symbol (and) is a logical operator, and is used to combine conditional statements:

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OR

The | symbol (or) is a logical operator, and is used to combine conditional statements:

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R While Loop

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Loops

Loops can execute a block of code as long as a specified condition is reached.

Loops are handy because they save time, reduce errors, and they make code more readable.

R has two loop commands:

• while loops
• for loops

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R While Loops

With the while loop we can execute a set of statements as long as a condition is TRUE:

In the example above, the loop will continue to produce numbers ranging from 1 to 5. The loop will stop at 6 because 6 < 6 is FALSE.

The while loop requires relevant variables to be ready, in this example we need to define an indexing variable, i, which we set to 1.

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Break

With the break statement, we can stop the loop even if the while condition is TRUE:

The loop will stop at 3 because we have chosen to finish the loop by using the break statement when i is equal to 4 (i == 4).

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Next

With the next statement, we can skip an iteration without terminating the loop:

When the loop passes the value 3, it will skip it and continue to loop.

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Yahtzee!

If .. Else Combined with a While Loop

To demonstrate a practical example, let us say we play a game of Yahtzee!

If the loop passes the values ranging from 1 to 5, it prints “No Yahtzee”. Whenever it passes the value 6, it prints “Yahtzee!”.

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R For Loop

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For Loops

A for loop is used for iterating over a sequence:

This is less like the for keyword in other programming languages, and works more like an iterator method as found in other object-orientated programming languages.

With the for loop we can execute a set of statements, once for each item in a vector, array, list, etc..

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Break

With the break statement, we can stop the loop before it has looped through all the items:

The loop will stop at “cherry” because we have chosen to finish the loop by using the break statement when x is equal to “cherry” (x == "cherry").

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Next

With the next statement, we can skip an iteration without terminating the loop:

When the loop passes “banana”, it will skip it and continue to loop.

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Yahtzee!

If .. Else Combined with a For Loop

To demonstrate a practical example, let us say we play a game of Yahtzee!

If the loop reaches the values ranging from 1 to 5, it prints “No Yahtzee” and its number. When it reaches the value 6, it prints “Yahtzee!” and its number.

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Nested Loops

It is also possible to place a loop inside another loop. This is called a nested loop:

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Nested Functions

There are two ways to create a nested function:

• Call a function within another function.
• Write a function within a function.

Example Explained

The function tells x to add y.

The first input Nested_function(2,2) is “x” of the main function.

The second input Nested_function(3,3) is “y” of the main function.

The output is therefore (2+2) + (3+3) = 10.

Example Explained

You cannot directly call the function because the Inner_func has been defined (nested) inside the Outer_func.

We need to call Outer_func first in order to call Inner_func as a second step.

We need to create a new variable called output and give it a value, which is 3 here.

We then print the output with the desired value of “y”, which in this case is 5.

The output is therefore 8 (3 + 5).

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Recursion

R also accepts function recursion, which means a defined function can call itself.

Recursion is a common mathematical and programming concept. It means that a function calls itself. This has the benefit of meaning that you can loop through data to reach a result.

The developer should be very careful with recursion as it can be quite easy to slip into writing a function which never terminates, or one that uses excess amounts of memory or processor power. However, when written correctly, recursion can be a very efficient and mathematically-elegant approach to programming.

In this example, tri_recursion() is a function that we have defined to call itself (“recurse”). We use the k variable as the data, which decrements (-1) every time we recurse. The recursion ends when the condition is not greater than 0 (i.e. when it is 0).

To a new developer it can take some time to work out how exactly this works, best way to find out is by testing and modifying it.

Variables that are created outside of a function are known as global variables.

Global variables can be used by everyone, both inside of functions and outside.

If you create a variable with the same name inside a function, this variable will be local, and can only be used inside the function. The global variable with the same name will remain as it was, global and with the original value.

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The Global Assignment Operator

Normally, when you create a variable inside a function, that variable is local, and can only be used inside that function.

To create a global variable inside a function, you can use the global assignment operator <<-

Also, use the global assignment operator if you want to change a global variable inside a function: