I'm trying to compare two numbers in R as a part of a if-statement condition:
(a-b) >= 0.5
In this particular instance, a = 0.58 and b = 0.08... and yet (a-b) >= 0.5 is false. I'm aware of the dangers of using == for exact number comparisons, and this seems related:
(a - b) == 0.5) is false, while
all.equal((a - b), 0.5) is true.
The only solution I can think of is to have two conditions: (a-b) > 0.5 | all.equal((a-b), 0.5). This works, but is that really the only solution? Should I just swear off of the = family of comparison operators forever?
Edit for clarity: I know that this is a floating point problem. More fundamentally, what I'm asking is: what should I do about it? What's a sensible way to deal with greater-than-or-equal-to comparisons in R, since the >= can't really be trusted?
I've never been a fan of all.equal for such things. It seems to me the tolerance works in mysterious ways sometimes. Why not just check for something greater than a tolerance less than 0.05
tol = 1e-5
(a-b) >= (0.05-tol)
In general, without rounding and with just conventional logic I find straight logic better than all.equal
If x == y then x-y == 0. Perhaps x-y is not exactly 0 so for such cases I use
abs(x-y) <= tol
You have to set tolerance anyway for all.equal and this is more compact and straightforward than all.equal.