[R] Numbers that look equal, should be equal, but if() doesn't see as equal

[Paul Lemmens]

Hi!

After a lot of testing and debugging I'm falling silent in figuring out 
what goes wrong in the following.

I'm implementing the Vincentizing procedure that Ratcliff (1979) described. 
It's about calculating RT bins for any distribution of RT data. It boils 
down to rank ordering your data, replicating each data point as many times 
as you need bins and then splitting up the resulting distribution in equal 
bins.

The code that I've written is attached (and not included because it is 
considerable in length due to many comments). Ratcliff.r contains some 
basic functions and distribution.bins.r contains the problematic function 
bins.factor() (problem area marked with 'FAILING TEST'). The final attached 
file is the mock up distribution I made.

The failing test is the check if the mean of the mean RT's for each bin 
equals the mean of the original distribution. These should/are 
mathematically equivalent. Sometimes, however, the test fails. With the 
attached distribution most notably for 4, 7, 8, 9, and 13 bins. Since the 
means are mathematically equivalent IMHO it should not be an issue of this 
particular distribution. As a matter of fact, I also have tested some 
rnorm() distributions and my function also fails on those (albeit a little 
less often than with foobar.txt).

Problem description: if one calculates the bins or bin means by hand, the 
mean of the bin means is visually the same as the overall mean, even with 
options(digits=20), but *still* the test fails.

IMHO it's not my code and neither the distribution I use to test, but 
still, can you point out an obvious failure of my programming or is it 
indeed something of R that I don't yet grasp?

thank you for your help,
Paul


-- 
Paul Lemmens
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