[Rd] Date class shows Inf as NA; this confuses the use of is.na()

[Emil Bode]

I don't think there's much wrong with is.na(as_date(Inf, origin='1970-01-01'))==FALSE, as there still is some "non-NA-ness" about the value (as difftime shows), but that the output when printing is confusing. The way cat is treating it is clearer: it does print Inf.

So would this be a solution?

format.Date <- function (x, ...) 
{
  xx <- format(as.POSIXlt(x), ...)
  names(xx) <- names(x)
  xx[is.na(xx) & !is.na(x)] <- paste('Invalid date:',as.numeric(x[is.na(xx) & !is.na(x)]))
  xx
}

Which causes this behaviour, which I think is clearer:

environment(print.Date) <- .GlobalEnv
x <- as_date(Inf, origin='1970-01-01')
print(x)
# [1] "Invalid date: Inf"

Best regards, 
Emil Bode
 
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On 09/06/2018, 13:52, "R-devel on behalf of Joris Meys" <r-devel-bounces using r-project.org on behalf of jorismeys using gmail.com> wrote:

    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 using 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 using 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.
    >>
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    >>
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    >>
    >
    >
    >
    > --
    > Joris Meys
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    >
    > Department of Data Analysis and Mathematical Modelling
    > Ghent University
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    -- 
    Joris Meys
    Statistical consultant
    
    Department of Data Analysis and Mathematical Modelling
    Ghent University
    Coupure Links 653, B-9000 Gent (Belgium)
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