7 R: Variables, expression and statements

7.1 Style guide

We will use the tidyverse style guide for styling R code.

7.2 Data Types

Some of the commonly used objects in R are numbers - integer and double (or numeric), character and logical (TRUE/FALSE). The data type of the object can be identified using the in-built R function class() or typeof(). For example, see the following objects and their types:

class(4)

[1] "numeric"

typeof(4)

[1] "double"

class(4.4)

[1] "numeric"

typeof(4.4)

[1] "double"

class(4L)

[1] "integer"

typeof(4L)

[1] "integer"

class('4')

[1] "character"

typeof('4')

[1] "character"

class(TRUE)

[1] "logical"

typeof(FALSE)

[1] "logical"

7.3 Variable names

We have the following rules for a R variable name:

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…)

7.4 Converting datatypes

Sometimes a value may have a datatype that is not suitable for using it. For example, consider the variable called annual_income in the code below:

annual_income = "80000"

Suppose we wish to divide annual_income by 12 to get the monthly income. We cannot use the variable annual_income directly as its datatype is a string and not a number. Thus, numerical operations cannot be performed on the variable annual_income.

We’ll need to convert annual_income to an integer. For that we will use the R’s in-built as.integer() function:

annual_income = as.integer(annual_income)
monthly_income = annual_income/12
print(paste0("monthly income = ", monthly_income))

[1] "monthly income = 6666.66666666667"

Similarly, datatypes can be converted from one type to another using in-built R functions as shown below:

#Converting integer to character
as.character(9)

[1] "9"

#Converting character to numeric
as.numeric('9.4')

[1] 9.4

#Converting logical to integer
as.numeric(FALSE)

[1] 0

Note that any non-zero numeric value, if converted to the ‘logical’ datatype, will return TRUE, while converting 0 to the ‘logical’ datatype will return FALSE. Only numeric values can be converted to the ‘logical’ datatype.

# Converting integer to logical
as.logical(40)

[1] TRUE

# Converting integer to logical
as.logical(0)

[1] FALSE

# Converting integer to logical
as.logical(-30.1)

[1] TRUE

Sometimes, conversion of a value may not be possible. For example, it is not possible to convert the variable greeting defined below to a number:

greeting = "hello"

However, strings can be concatenated using the paste0() function:

paste0("hello", " there!")

[1] "hello there!"

R’s in-built readline() function can be used to accept an input from the user. For example, suppose we wish the user to input their age:

age = readline("Enter your age:")

Enter your age:

The entered value is stored in the variable age and can be used for computation.