is.logical() Function: Check If a Value is Logical in R

The is.logical() function in R checks whether an input object’s data type is logical. If the object is logical and its values are either TRUE or FALSE, it returns TRUE; otherwise, it returns FALSE.

This function checks the underlying type of the object. Due to the nature of the function, you can use it in conditional statements to validate user input.

Syntax

is.logical(obj)

Parameters

Testing basic values

logical_val_one <- TRUE
logical_val_two <- FALSE

is.logical(logical_val_one) # TRUE
is.logical(logical_val_two) # TRUE

You can see that TRUE and FALSE are logical values and return TRUE.

Let’s pass non-logical values and see the output:

is.logical(0) # FALSE

is.logical("hello") # FALSE

0 is the logical gate, but in R, it is a numeric value, so it returns FALSE.

Testing a Vector

If you create a vector that contains TRUE or FALSE values, this function returns TRUE.

vec_logical <- c(TRUE, FALSE, TRUE, FALSE)

is.logical(vec_logical) # TRUE

If you pass a non-logical vector, it returns FALSE.

non_logical_vec <- c(1, 2, 3, 4)

is.logical(non_logical_vec) # FALSE

Testing a List

The lists are not logical objects, so even if you pass all the elements of the list as logical values, it still returns FALSE.

list_obj <- list(TRUE, FALSE)

is.logical(list_obj) # FALSE

Testing NA (Not Available)

NA represents a missing value, and a missing value can be anything, including a logical type. 

So, if you pass NA to the is.logical() function, it returns TRUE.

is.logical(NA) # TRUE

Testing NaN (Not A Number)

NaN represents undefined numerical results, which means they are not logical values by default and cannot be converted to one. So, it returns FALSE.

is.logical(NaN) # FALSE

Testing NULL

NULL represents an empty object, which means there is nothing, including logical values. Hence, it returns FALSE.

is.logical(NULL) # FALSE

That’s all!