Checking if variable is set or not

[pathos]

Not exactly a game-breaking bug, but I was curious on how people generally would deal with this.

I have set a list variable that is initialised with a default value of NA. But, this value gets replaced with a list (so list within a list) if the user sets the value.

So when I put this into an if statement, it will only check for the first element in the list:

if (!is.na(list1$list2)) {
  ...
}
# the condition has length > 1 and only the first element will be used

So the potential problem is if the first element is, by off chance, NA. It won't be 99% of the time, but I'm trying to prevent the exception.

I just want to check if the variable has been altered or not from the initial state. What would be the right solution for this?

[pieterjanvc]

Hi there,

I find the logic a bit weird, but that's probably because I don't know the larger context. Whenever I need to set a variable and then later check for it, I use the NULL which will create an empty object. So whatever the user inputs (including NA and regardless of the number of items) will be different.

myList = NULL

if(is.null(myList)){
  print("Empty")
} else {
  print("Not empty")
}
#> [1] "Empty"


myList = list(NA, list(5))

if(is.null(myList)){
  print("Empty")
} else {
  print("Not empty")
}
#> [1] "Not empty"

^{Created on 2022-03-09 by the reprex package (v2.0.1)}

Hope this helps,
PJ

[pathos]

Ah thanks, but I should have mentioned that it must be NA, not NULL. I'm unsure if the same logic would be applicable for NULL -- they are handled differently.

[pieterjanvc]

HI,

That is exactly why I suggested this solution. Could you provide an actual example where this issue surfaces, because I don't understand what it is you want now

Try and create a reprex. A reprex consists of the minimal code and data needed to recreate the issue/question you're having. You can find instructions how to build and share one here:

FAQ: How to do a minimal reproducible example ( reprex ) for beginners

A minimal reproducible example consists of the following items: A minimal dataset, necessary to reproduce the issue The minimal runnable code necessary to reproduce the issue, which can be run on the given dataset, and including the necessary information on the used packages. Let's quickly go over each one of these with examples: Minimal Dataset (Sample Data) You need to provide a data frame that is small enough to be (reasonably) pasted on a post, but big enough to reproduce your issue. Let's say, as an example, that you are working with the iris data frame head(iris) #> Sepal.Length Sepal.Width Petal.Length Petal.Width Species #> 1 5.1 3.5 1.4 0.…

Good luck