[R] julian() and numerical noise

[Andreas Eckner]

Thanks for the help. A workaround seems indeed easy to write, for 
example, by rounding the the value of 'm' inside 
chron:::julian.default(), or only passing integers to the function.

I never intended to use a case involving a quadrillionth of a day, but 
encountered the problem when converting a dates in YYYY.MM format to a 
CHRON object. Here is an example for future reference (the output might 
be highly system-dependent):

 >   library(chron)
 >   date <- 2012.02
 >   y <- floor(date)
 >   m <- (date %% 1) * 100
 >   julian(2, 1, 2012) - julian(m, 1, y)
[1] 1

~Andreas

P.S.: I have included Kurt Hornik on the email.

On 3/23/2012 10:52 PM, R. Michael Weylandt wrote:
> julian() is in the package base. chron only provides julian.default to
> avoid the error Uwe observed. If you look at the code for
> julian.default, it's not too hard to see why date will be slightly
> more sensitive to "numeric fuzz"....whether that's intentional (or
> even a good/bad thing) is somewhat hard to say, but I'd guess the
> maintainer didn't really consider a use case involving one
> quadrillionth of a day.
>
> Is it problematic for you? If so, a workaround is not hard to provide
>
> Michael
>
> On Fri, Mar 23, 2012 at 4:17 PM, Andreas Eckner<andreas at eckner.com>  wrote:
>> Sorry, forgot to mention: R version 2.14.2
>>
>> The function julian() is part of the "chron" package of the base
>> distribution.
>>
>> On 3/23/2012 2:47 PM, Uwe Ligges wrote:
>>> On 23.03.2012 15:45, Andreas Eckner wrote:
>>>> Hi,
>>>>
>>>> does anybody know if the following behavior of julian() is intentional?
>>>>
>>>>> julian(2, 1, 2012) - julian(2 - 1e-15, 1, 2012)
>>>> [1] 1
>>>>> julian(2, 1, 2012) - julian(2, 1 - 1e-15, 2012)
>>>> [1] 0
>>>>> julian(2, 1, 2012) - julian(2, 1, 2012 - 1e-15)
>>>> [1] 0
>>>>
>>>> In other words, julian() is subject to numerical noise in the 'day'
>>>> argument, but not in the 'month' and 'year' argument? Another example:
>>>>
>>>>> julian(2 - 1e-15, 1, 2012) - julian(1 - 1e-15, 1, 2012)
>>>> [1] 30
>>>
>>>
>>> Which vbersion of R are you talking about?
>>>
>>> I get:
>>>
>>>> julian(2, 1, 2012) - julian(2 - 1e-15, 1, 2012)
>>> Error in UseMethod("julian") :
>>>   no applicable method for 'julian' applied to an object of class
>>> "c('double', 'numeric')"
>>>
>>>
>>> Uwe Ligges
>>>
>>>
>>>> Thanks,
>>>> Andreas
>>>>
>>>> ______________________________________________
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>>>> https://stat.ethz.ch/mailman/listinfo/r-help
>>>> PLEASE do read the posting guide
>>>> http://www.R-project.org/posting-guide.html
>>>> and provide commented, minimal, self-contained, reproducible code.
>>>
>>>
>> ______________________________________________
>> R-help at r-project.org mailing list
>> https://stat.ethz.ch/mailman/listinfo/r-help
>> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
>