[R] Cause of error assigning NULL to element of a vector

[Marc Schwartz]

> On May 24, 2017, at 1:30 PM, Ramnik Bansal <ramnik.bansal at gmail.com> wrote:
> 
> What is the cause of the error below ?
> 
>> y <- 1
>> y[1] <- NULL
> Error in y[1] <- NULL : replacement has length zero
> 
> Thanks,
> Ramnik

Hi,

> length(NULL)
[1] 0

You are attempting to assign NULL, which is a zero length special object of its own kind, to a specific element in the vector object 'y' and that cannot be done.

You can assign NULL to 'y':

y <- NULL

> y
NULL

> length(y)
[1] 0


BUT, 'y' is not a vector in that case:

> is.vector(y)
[1] FALSE



Nor can a vector contain multiple NULLs:

y <- c(NULL, NULL, NULL)

> y
NULL

> length(y)
[1] 0



Similarly:

y <- c(1, NULL, 1)

> y
[1] 1 1

> length(y)
[1] 2


Perhaps reviewing ?NULL as well as:

  https://cran.r-project.org/doc/manuals/r-release/R-lang.html#NULL-object

might also provide some insights.

Regards,

Marc Schwartz