Question

R programming: code

4. _what is the difference between logical(0) and NULL? write a command (other than ogical(0) that will produce logical (0) as the output. Write a command (other than NULL that will produce NULL as the output._

Answer 1

NULL basically means no value, or unknown, and it should not be confused with 0 which is a numeric value by itself. NULL value could be either empty, meaningless, or not even initialized. Eg: If value of a variable is NULL means that the variable is not defined while when it’s value is 0 means it is 0 value.

A zero length vectors can have attributes, whereas NULL cannot have attributes

R Command for logical(0) is:

which(!is.na(c(NA,NA,NA))) == 0

Output:

Logical(0)

R Command for NULL is:

Class(NULL)

Output:

NULL

Or

li <- list( 1, 2, 3 )

li$aa

Output:

NULL