R devel - Jun 2018 - Date class shows Inf as NA; this confuses the use of is.na()

Indeed. as_date is from lubridate, but the same holds for as.Date.

The output and it's interpretation should be consistent, otherwise it leads
to confusion when programming. I understand that the difference exists
after asking a question on Stack Overflow:
  https://stackoverflow.com/q/50766089/914686
This understanding is never mentioned in the documentation - that an Inf
date is actually represented as NA:
  https://www.rdocumentation.org/packages/base/versions/3.5.0/topics/as.Date
So I'm of the impression that the display should be fixed as a first option
(thereby providing clarity/transparency in terms of back-end and output),
or the documentation amended (to highlight this) as a second option.

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Hi Werner,

on ?is.na it says:
> The default method for anyNA handles atomic vectors without a class and
NULL.

I hear you, and it is confusing to say the least. Looking deeper, the
culprit seems to be in the conversion of a Date to POSIXlt prior to the
formatting:
> x <- as.Date(Inf,origin = '1970-01-01')
> is.na(as.POSIXlt(x))
[1] TRUE

Given this implicit conversion, I'd argue that as.Date should really return
NA as well when passed an infinite value. The other option is to provide an
is.na method for the Date class, which is -given is.na is an internal
generic- rather trivial:
> is.na.Date <- function(x) is.na(as.POSIXlt(x))
> is.na(x)
[1] TRUE

This might be a workaround for your current problem without needing changes
to R itself. But this will give a "wrong" answer in the sense that
this
still works:
> Sys.Date() - x
Time difference of -Inf days

I personally would go for NA as the "correct" date for an infinite
value,
but given that this will have implications in other areas, there is a
possibility of breaking code and it should be investigated a bit further
imho.
Cheers
Joris




On Fri, Jun 8, 2018 at 11:21 PM, Werner Grundlingh <wgrundlingh at
gmail.com>
wrote:
> Indeed. as_date is from lubridate, but the same holds for as.Date.
>
> The output and it's interpretation should be consistent, otherwise it
leads
> to confusion when programming. I understand that the difference exists
> after asking a question on Stack Overflow:
>   https://stackoverflow.com/q/50766089/914686
> This understanding is never mentioned in the documentation - that an Inf
> date is actually represented as NA:
>   https://www.rdocumentation.org/packages/base/versions/3.
> 5.0/topics/as.Date
> So I'm of the impression that the display should be fixed as a first
option
> (thereby providing clarity/transparency in terms of back-end and output),
> or the documentation amended (to highlight this) as a second option.
>
>         [[alternative HTML version deleted]]
>
> ______________________________________________
> R-devel at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel
>


-- 
Joris Meys
Statistical consultant

Department of Data Analysis and Mathematical Modelling
Ghent University
Coupure Links 653, B-9000 Gent (Belgium)
<https://maps.google.com/?q=Coupure+links+653,%C2%A0B-9000+Gent,%C2%A0Belgium&entry=gmail&source=g>

-----------
Biowiskundedagen 2017-2018
http://www.biowiskundedagen.ugent.be/

-------------------------------
Disclaimer : http://helpdesk.ugent.be/e-maildisclaimer.php

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And now I've seen I copied the wrong part of ?is.na
> The default method for is.na applied to an atomic vector returns a
logical vector of the same length as its argument x, containing TRUE for
those elements marked NA or, for numeric or complex vectors, NaN, and FALSE
otherwise.

Key point being "atomic vector" here.


On Sat, Jun 9, 2018 at 1:41 PM, Joris Meys <jorismeys at gmail.com> wrote:
> Hi Werner,
>
> on ?is.na it says:
>
> > The default method for anyNA handles atomic vectors without a class
and
> NULL.
>
> I hear you, and it is confusing to say the least. Looking deeper, the
> culprit seems to be in the conversion of a Date to POSIXlt prior to the
> formatting:
>
> > x <- as.Date(Inf,origin = '1970-01-01')
> > is.na(as.POSIXlt(x))
> [1] TRUE
>
> Given this implicit conversion, I'd argue that as.Date should really
> return NA as well when passed an infinite value. The other option is to
> provide an is.na method for the Date class, which is -given is.na is an
> internal generic- rather trivial:
>
> > is.na.Date <- function(x) is.na(as.POSIXlt(x))
> > is.na(x)
> [1] TRUE
>
> This might be a workaround for your current problem without needing
> changes to R itself. But this will give a "wrong" answer in the
sense that
> this still works:
>
> > Sys.Date() - x
> Time difference of -Inf days
>
> I personally would go for NA as the "correct" date for an
infinite value,
> but given that this will have implications in other areas, there is a
> possibility of breaking code and it should be investigated a bit further
> imho.
> Cheers
> Joris
>
>
>
>
> On Fri, Jun 8, 2018 at 11:21 PM, Werner Grundlingh <wgrundlingh at
gmail.com>
> wrote:
>
>> Indeed. as_date is from lubridate, but the same holds for as.Date.
>>
>> The output and it's interpretation should be consistent, otherwise
it
>> leads
>> to confusion when programming. I understand that the difference exists
>> after asking a question on Stack Overflow:
>>   https://stackoverflow.com/q/50766089/914686
>> This understanding is never mentioned in the documentation - that an
Inf
>> date is actually represented as NA:
>>   https://www.rdocumentation.org/packages/base/versions/3.5.0/
>> topics/as.Date
>> So I'm of the impression that the display should be fixed as a
first
>> option
>> (thereby providing clarity/transparency in terms of back-end and
output),
>> or the documentation amended (to highlight this) as a second option.
>>
>>         [[alternative HTML version deleted]]
>>
>> ______________________________________________
>> R-devel at r-project.org mailing list
>> https://stat.ethz.ch/mailman/listinfo/r-devel
>>
>
>
>
> --
> Joris Meys
> Statistical consultant
>
> Department of Data Analysis and Mathematical Modelling
> Ghent University
> Coupure Links 653, B-9000 Gent (Belgium)
>
>
<https://maps.google.com/?q=Coupure+links+653,%C2%A0B-9000+Gent,%C2%A0Belgium&entry=gmail&source=g>
>
> -----------
> Biowiskundedagen 2017-2018
> http://www.biowiskundedagen.ugent.be/
>
> -------------------------------
> Disclaimer : http://helpdesk.ugent.be/e-maildisclaimer.php
>


-- 
Joris Meys
Statistical consultant

Department of Data Analysis and Mathematical Modelling
Ghent University
Coupure Links 653, B-9000 Gent (Belgium)
<https://maps.google.com/?q=Coupure+links+653,%C2%A0B-9000+Gent,%C2%A0Belgium&entry=gmail&source=g>

-----------
Biowiskundedagen 2017-2018
http://www.biowiskundedagen.ugent.be/

-------------------------------
Disclaimer : http://helpdesk.ugent.be/e-maildisclaimer.php

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