Relational Operators in R

In this tutorial you will learn about the Relational operators (also known as comparison operators) in R and how to use them. Like most of the programming languages, R programming also has relational operators to check the relationship between two operands. If the relation is true, then it returns the logical value TRUE; if the relation is false, then it returns the logical value FALSE.

Relational Operators in R

Following symbols are used as relational operators in R programming language:

Operator Symbols	Relational Operation	Example
$==$	Is Equal	$10 == 5$ returns FALSE
$!=$	Is Not equal	$10 != 5$ returns TRUE
$<$	Is Less than	$10 < 5$ returns FALSE
$>$	Is Greater than	$10 > 5$ returns TRUE
$<=$	Is Less than or equal	$10 <= 5$ returns FALSE
$>=$	Is Greater than or equal	$10 >= 5$ returns TRUE

Note than the output of relational operation contains the boolean values (TRUE or FALSE) based on the relational operator.

Examples of Relational Operators

To understand the use of relational operators, let us discuss some examples.

Equal to

10 == 5

[1] FALSE

Above R command check whether 10 equal to 5. Since 10 is not equal to 5, R returns FALSE.

Not Equal to

10 != 5

[1] TRUE

Above R command check whether 10 is not equal to 5. Since 10 is not equal to 5, R returns TRUE.

Less Than

10 < 5

[1] FALSE

Above R command check whether 10 is less than 5. Since 10 is not less than 5, R returns FALSE.

Greater Than

10 > 5

[1] TRUE

Above R command check whether 10 is greater than 5. Since 10 is greater than 5, R returns TRUE.

Less Than or Equal

10 <= 5

[1] FALSE

Above R command check whether 10 less than or equal to 5. Since 10 is not less than or equal to 5, R returns FALSE.

Greater Than or Equal

10 >= 5

[1] TRUE

Above R command check whether 10 greater than or equal to 5. Since 10 is greater than or equal to 5, R returns TRUE.

Relational operations on Vector and scalar

Like arithmetic operators, relational operations are also vectorized. When vector is compared with scalar using relational operator, R will recycled the scalar element to the length of vector and then perform element-wise relational operations.

# Create a vector x
x <- c(12, 10, 8, 16, 6)
x < 8

[1] FALSE FALSE FALSE FALSE  TRUE

x == 10

[1] FALSE  TRUE FALSE FALSE FALSE

x <= 8

[1] FALSE FALSE  TRUE FALSE  TRUE

Note than in all the above R codes, the left side of relational operator is a vector and right side of is a scalar. In such a case R recycle the scalar to match the length of vector and then perform the element-wise relational operation.

Relational operators can also be used to extract the elements of a vector based on some relational expression.

Suppose we need to extract only those elements of x which are less than 8. To do this we can use following R code:

x <- c(12, 10, 8, 16, 6)
x[x > 8]

[1] 12 10 16

Above code extract only those elements of x which are greater than 8.

x[x != 10]

[1] 12  8 16  6

Above code extract only those elements of x which are not equal to 10.

x[x <= 8]

[1] 8 6

Above code extract only those elements of x which are less than or equal to 8.

Relational operations on Vectors of equal length

If the length of both the operand in relational expression is same, R will check the relation element-wise.

x <- c(12, 10, 8, 16, 6)
y <- c(10, 12, 8, 18, 6)

# Are x and y equal (element-wise)?
x == y

[1] FALSE FALSE  TRUE FALSE  TRUE

# Are x less than equal to y-2 (element-wise)?
x <= y - 2

[1] FALSE  TRUE FALSE  TRUE FALSE

Relational operations on Vectors of unequal length

Recycling rule also work while comparing a shorter vector with a longer vector. R will recycle the elements of shorter vector and then perform the relational operation element-wise.

x <- c(10, 20, 6, 25)
y <- c(4, 20, 8)

As y is shorter than x, R will recycled the elements of shorter vector y as (4,20,8,4) and then perform the relational operations element-wise.

# Are x and y equal (element-wise)?
x == y

Warning in x == y: longer object length is not a multiple of shorter object
length

[1] FALSE  TRUE FALSE FALSE

# Are x less than y (element-wise)?
x < y

Warning in x < y: longer object length is not a multiple of shorter object
length

[1] FALSE FALSE  TRUE FALSE

# Are x less than or equal to y (element-wise)?
x <= y

Warning in x <= y: longer object length is not a multiple of shorter object
length

[1] FALSE  TRUE  TRUE FALSE

# Are x not equal to y (element-wise)?
x != y

Warning in x != y: longer object length is not a multiple of shorter object
length

[1]  TRUE FALSE  TRUE  TRUE

Note than the output of relational operation on vectors will be another vector of same length and will contain the boolean values (TRUE or FALSE) based on the element-wise comparison.

Endnote

In this tutorial you learned about relational operators in R and how R uses recycling rule while performing relational operations.

To learn more about other operators in R, please refer to the following tutorials:

Assignment operators in R
Arithmetic operators in R
Logical operators in R
Miscellaneous operators in R
Precendence of Operators in R
Operators in R

Hopefully you enjoyed learning this tutorial on relational operators in R. Hope the content is more than sufficient to understand relational operators in R.