Question

Consider the following vector a

a <- c(NULL, 1, 2, "A", NULL, NA)

I am trying to identify the positions of NULL in the vector. However, NULL is not a string. I am wondering why is.null does not work similar to is.na which returns the positions of the NAs in the vector.

> is.na(a)
[1] FALSE FALSE FALSE  TRUE
> is.null(a)
[1] FALSE

Answer 1

The function is.null is used to check whether an object is identical to NULL. The NULL values are not part of the vector, they are “nothing”.

Hence your vector does not include any NULLs but the other values only:

[1] "1" "2" "A" NA

The information about the NULLs you used to create the vector is lost and cannot be retrieved.