alternative to "!is.null()" in R

user_183988 0
Viewed 147800

my R code ends up containing plethora of statements of the form:

if (!is.null(aVariable)) { 
     do whatever 
}

But this kind of statement is hard to read because it contains two negations. I would prefer something like: 

 if (is.defined(aVariable)) { 
      do whatever 
 }

Does a is.defined type function that does the opposite of !is.null exist standard in R?

cheers, yannick

r
6 Answers

You may be better off working out what value type your function or code accepts, and asking for that:

if (is.integer(aVariable))
{
  do whatever
}

This may be an improvement over isnull, because it provides type checking. On the other hand, it may reduce the genericity of your code.

Alternatively, just make the function you want:

is.defined = function(x)!is.null(x)
user_1213320

If it's just a matter of easy reading, you could always define your own function :

is.not.null <- function(x) !is.null(x)

So you can use it all along your program.

is.not.null(3)
is.not.null(NULL)
user_1716590

Ian put this in the comment, but I think it's a good answer:

if (exists("aVariable"))
{
  do whatever
}

note that the variable name is quoted.

user_377510

I have also seen: 

if(length(obj)) {
  # do this if object has length
  # NULL has no length
}

I don't think it's great though. Because some vectors can be of length 0. character(0), logical(0), integer(0) and that might be treated as a NULL instead of an error.

user_1703520

To handle undefined variables as well as nulls, you can use substitute with deparse:

nullSafe <- function(x) {
  if (!exists(deparse(substitute(x))) || is.null(x)) {
    return(NA)
  } else {
    return(x)
  }
}

nullSafe(my.nonexistent.var)
user_4330610
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