[R] cut2 not binning interval endpoints correctly

S Ellison S.Ellison at LGCGroup.com
Wed Nov 27 18:12:28 CET 2013

> -----Original Message-----
>jim holtman <jholtman at gmail.com>
> You need to look at the full accuracy of the number representation:
Um... I think I did. But I'm not sure you did.... 
print(..., digits=20) has used different numbers of digits for your two print()s, probably because print() decided it needed more digits for the multi-valued vector. The internal representations were the same. Try

print(seq(0, 0.310, 0.001)[309], digits = 20)
[1] 0.307999999999999996

print(seq(0, 0.310, 0.001)[309], digits = 22)
[1] 0.3079999999999999960032

> print(0.308, digits = 22)
[1] 0.3079999999999999960032

0.308 does match the cut boundary 'exactly' in this case (which is why the usually unwise '==' returned TRUE), though neither is exactly 0.308. 

Nonetheless, I understand that FAQ 7.31 is a good candidate for other 'unexpected' cut2 results. However, that isn't the whole story. It doesn't explain the corresponding cut(, right=FALSE) result, which should give the same answer as cut2 if finite representation were the sole cause. So there's summat else going on.

Steve E

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