[R] choose() function returning anomalous results (zero instead of one)

[Duncan Murdoch]

On 06/09/2012 2:09 PM, Shayne Hodge wrote:
> Hello,
>
> (Apologies for length, wanted to get all the relevant detail in that I know
> of).
>
> I've been having a lot of trouble with some code for an inventory analysis
> problem I was doing, and finally came to the conclusion that it appears
> that choose() is returning incorrect values. Specifically:
>
> -------------
>
> Browse[1]> nn
> [1] 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 3 3 3 3 3 3 3
> Browse[1]> Q1
> [1] 3
> Browse[1]> choose(Q1,3)
> [1] 0

That's easy to reproduce, with correct behaviour:

 > Q1 <- 3 - 1e-10
 > Q1
[1] 3
 > choose(Q1, 3)
[1] 0

My guess is your code (which is tl;dr) computes Q1 with some rounding 
error, and you're seeing something like this.

Duncan Murdoch