What is NULL Object in R

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NULL in R is a special object that represents the absence of any object. It is often used as a placeholder or to indicate the absence of a value.

NULL is used largely to represent the lists with zero length and is usually returned by expressions and functions whose value is undefined.

Example 1: How to define a NULL in R

To create a NULL, assign it to a variable, and that variable becomes NULL.

rv <- NULL
rv
typeof(rv)

Output

NULL
[1] "NULL"

Example 2: Using NULL as a placeholder

main_function <- function() {
  return(NULL)
}

# call the function and assign the result to a variable
null_res <- main_function()

# print the result
print(null_res)

Output

NULL

R provides two functions to deal with NULL.

  1. is.null()
  2. as.null()

is.null() function in R

The is.null() is a built-in R function that checks whether the variable has a NULL value. It returns the logical vector, either TRUE or FALSE.

rv <- NULL
rv
is.null(rv)

Output

NULL
[1] TRUE

Let’s define a list of mixed values, including NULL value, and use the is.null() function to see the output.

rl <- list(1, 2, NULL, 4, 5)
rl
cat("Checking the NULL value", "\n")
is.null(rl)

Output

[[1]]
[1] 1

[[2]]
[1] 2

[[3]]
NULL

[[4]]
[1] 4

[[5]]
[1] 5

Checking the NULL value
[1] FALSE

You can see from the output that it is.null() function returns FALSE.

Let’s check the same for the vector in R to see if we get the same output.

rv <- c(1, NULL, 2, 4, 3)
rv
cat("Checking the NULL value of Vector", "\n")
is.null(rv)

Output

[1] 1 2 4 3
Checking the NULL value of Vector
[1] FALSE

And we get the FALSE in the output, but let’s fill all the values with NULL and use the is.null() function again!

rv <- c(NULL, NULL, NULL, NULL, NULL)
rv
cat("Checking the NULL value of Vector", "\n")
is.null(rv)

Output

NULL
Checking the NULL value of Vector
[1] TRUE

Surprise! It returns TRUE, meaning if all the vector elements are NULL, it is.null() returns TRUE.

You can check if a variable is NULL by using the is.null() function, which returns TRUE if its argument is NULL and FALSE otherwise.

as.null() function in R

You can convert a variable to NULL by using the as.null() function, which ignores its argument and returns the value NULL. The as.null() function ignores its argument and returns the value NULL.

Syntax

as.null(x, ...)

Parameters

The x is an object to be tested or coerced.
The … will be ignored.

Example

rv <- c(1, 2, 3, 4, 5)
rv
cat("Converting a vector to NULL", "\n")
rv_null <- as.null(rv)
rv_null
is.null(rv_null)

Output

[1] 1 2 3 4 5
Converting a vector to NULL
NULL
[1] TRUE

As we can see that the as.null() function converts R Vector to NULL. This way, you can create any data type to NULL by assigning the value NULL or using the as.null() function to convert it to NULL.

See also

NaN in R

NA in R

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