Logical Tests

Logical tests are used extensively in coding in general, and coding in R is no exception. By a logical test, we mean an expression that evaluates to either TRUE or FALSE (or sometimes NA).

Comparison operators

Certain logical tests (but not all) involve the use of comparison operators. The most common comparison operators are:

Column details
Operator	Description	Example	Result
`==`	Equal to	`x == 5`	`TRUE` if `x` is 5, otherwise `FALSE`
`!=`	Not equal to	`x != 5`	`TRUE` if `x` is not 5, otherwise `FALSE`
`<`	Less than	`x < 5`	`TRUE` if `x` is less than 5, otherwise `FALSE`
`>`	Greater than	`x > 5`	`TRUE` if `x` is greater than 5, otherwise `FALSE`
`<=`	Less than or equal to	`x <= 5`	`TRUE` if `x` is less than or equal to 5, otherwise `FALSE`
`>=`	Greater than or equal to	`x >= 5`	`TRUE` if `x` is greater than or equal to 5, otherwise `FALSE`

Let’s pick apart a few of these for a moment:

== – Why can’t we just use =? Although we’ve been using <- for assignment in R, but = can also be used for assignment. So, we need a different operator, ==, when we want to compare whether two values are equal.

!= – This operator checks if two values are not equal. It is the opposite of ==. Notice that ! is used to indicate negation, and we can also use it to turn TRUE into FALSE and vice versa.

<, >, <=, >= – These operators are used not only to compare numerical values, but they can also be used to compare character data (for example, 'aa' < 'ab' is TRUE) and date values (for example, as.Date('2025-01-01') > as.Date('2023-07-06') is TRUE)

Logical tests on vectors and matrices

When we use comparison operators on vectors or matrices, R will perform the comparison element-wise. For example:

# Vector example
x <- c(1, 2, 3, 4, 5)
x > 3

[1] FALSE FALSE FALSE  TRUE  TRUE

# Matrix example - first create the matrix
x <- matrix(c(1, 2, 3, 4, 5, 6), nrow = 2)
x

     [,1] [,2] [,3]
[1,]    1    3    5
[2,]    2    4    6

# Matrix example - perform the test
x >= 4

      [,1]  [,2] [,3]
[1,] FALSE FALSE TRUE
[2,] FALSE  TRUE TRUE

There’s also a special operator, %in%, that we can use to return a TRUE or FALSE depending on whether a particular value is or is not present in a vector or matrix:

names <- c('Ali', 'Bob', 'Charlotta')
'Divya' %in% names

[1] FALSE

The many uses of logical tests

Logical tests are used in conditional statements, such as if statements, and in loops, such as for and while loops. They are also used in subsetting data frames and vectors.