[Rd] max on numeric_version with long components

[Kurt Hornik]

>>>>> Ivan Krylov via R-devel writes:

Indeed, apparently using which.min/which.max on the string encoding is
not good enough.  ? which.min says that x can also be

  an R object for which the internal coercion to ‘double’ works 

and I guess we found a case where it does not work.

I'll look into fixing this, but perhaps we should re-open
<https://bugs.r-project.org/show_bug.cgi?id=18697> ?

-k

> В Sat, 27 Apr 2024 13:56:58 -0500
> Jonathan Keane <jkeane using gmail.com> пишет:

>> In devel:
>> > max(numeric_version(c("1.0.1.100000000", "1.0.3.100000000",  
>> "1.0.2.100000000")))
>> [1] ‘1.0.1.100000000’
>> > max(numeric_version(c("1.0.1.10000000", "1.0.3.10000000",  
>> "1.0.2.10000000")))
>> [1] ‘1.0.3.10000000’

> Thank you Jon for spotting this!

> This is an unintended consequence of
> https://bugs.r-project.org/show_bug.cgi?id=18697.

> The old behaviour of max(<numeric_version>) was to call
> which.max(xtfrm(x)), which first produced a permutation that sorted the
> entire .encode_numeric_version(x). The new behavioiur is to call
> which.max directly on .encode_numeric_version(x), which is faster (only
> O(length(x)) instead of a sort).

> What do the encoded version strings look like?

> x <- numeric_version(c(
>  "1.0.1.100000000", "1.0.3.100000000", "1.0.2.100000000"
> ))
> # Ignore the attributes
> (e <- as.vector(.encode_numeric_version(x)))
> # [1] "000000001000000000000000001575360400"
> # [2] "000000001000000000000000003575360400"
> # [3] "000000001000000000000000002575360400"

> # order(), xtfrm(), sort() all agree that e[2] is the maximum:
> order(e)
> # [1] 1 3 2
> xtfrm(e)
> # [1] 1 3 2
> sort(e)
> # [1] "000000001000000000000000001575360400"
> # [2] "000000001000000000000000002575360400"
> # [3] "000000001000000000000000003575360400"

> # but not which.max:
> which.max(e)
> # [1] 1

> This happens because which.max() converts its argument to double, which
> loses precision:

> (n <- as.numeric(e))
> # [1] 1e+27 1e+27 1e+27
> identical(n[1], n[2])
> # [1] TRUE
> identical(n[3], n[2])
> # [1] TRUE

> Will be curious to know if there is a clever way to keep both the O(N)
> complexity and the full arbitrary precision.

> -- 
> Best regards,
> Ivan

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