How to use numeric(0) in greater than testing?

Question

I'm running a greater than test (see below) in a for loop:

if(x > y){...}

but at one point y will become numeric(0) while x will still be a numeric. So I need to know if there is a way to still test if a number is greater than numeric(0). This is the error message I get when I do it:

Error in if (x > y) { : 
  argument is of length zero

Is there a way to test it or even a way to substitute just plain 0 for numeric(0) in this case?

Thanks

Answer 1

What is supposed to happen when you compare a number with an empty value? Should the condition x > y evaluate to TRUE or FALSE, or should there be a different effect? One way to handle the situation is like this:

if (length(y) == 0) {
    cat("y is numeric(0)")
} else {
    if (x > y) {
        cat("x is greater than y")
    } else {
        cat("x is less than or equal y")
    }
}

Answer 2

Another approach, depending (as BigFinger wrote) on what you want the branching to be,

if(length(x)>0 && x>y ) {do_your_stuff}

I am assuming here that your x and y are scalars. Otherwise, you'll need to be a lot more careful, as if doesn't accept a multiple-valued outcome.

Answer 3

If x and y are always scalars or numeric(0), and if numeric(0) is equivalent to 0 in your problem, then you can write

if(sum(x) > sum(y)){...}

or leaving x without the sum if you know it can never become numeric(0).

This works because sum(numeric(0)) gives 0.

I haven't tested whether this is faster than implementing an if that checks the length of y, but I believe it should be faster (and more concise).