Never mind... the solution was to read the source code of
as.Date.character. It turns out the default format="" is meaningless.
If 'format' is not given in the call to as.Date, it is NOT assumed to
be "", and the function gives very different results from a call where
the argument format="" is given. Grrrr...
Peter
On Wed, Aug 20, 2014 at 11:56 AM, Peter Langfelder
<peter.langfelder at gmail.com> wrote:> Hi all,
>
> I have recently started working with Date objects and find the
> experience unsettling, to put it mildly.
>
> The help for as.Date says, in part:
>
> ## S3 method for class 'character'
> as.Date(x, format = "", ...)
>
> x: An object to be converted.
>
> format: A character string. If not specified, it will try
> ?"%Y-%m-%d"? then ?"%Y/%m/%d"? on the first
non-?NA? element,
> and give an error if neither works.
>
>
> If I read this correctly,
>
> as.Date("2012-04-30") and
> as.Date("2012-04-30", format = "")
>
> should give the same results, but they don't:
>
>> as.Date("2012-04-30")
> [1] "2012-04-30"
>> as.Date("2012-04-30", format = "")
> [1] "2014-08-20"
>
> Note the latter gives today's date, without any warning or message.
>
> What method is called in the latter case?
>
> Another issue I am running into, that is probably connected to the
> 'format' argument above, is trying to convert a numeric or
character
> in the same call. Basically, I would like to call
>
> as.Date(object, format = "", origin = "1970-1-1")
>
> where object can be a Date, numeric or character, in the hope that the
> appropriate method will be selected and will ignore unnecessary
> arguments.
>
> Here's what I get:
>
>> as.Date( as.numeric(Sys.Date()), origin = "1970-1-1")
> [1] "2014-08-20" #### Correct
>> as.Date( as.numeric(Sys.Date()), origin = "1970-1-1", format
= "")
> [1] "2059-04-08" #### ???
>
> Excuse the coarse language, but WTF??? The first call confirms that
> the origin is specified correctly, and the second gives a date removed
> from the origin by twice the number of days than the actual input??
>
>> as.numeric(Sys.Date())
> [1] 16302
>> as.numeric(as.Date( as.numeric(Sys.Date()), origin =
"1970-1-1"))
> [1] 16302
>> as.numeric(as.Date( as.numeric(Sys.Date()), origin =
"1970-1-1", format = ""))
> [1] 32604
>
>
> Thanks in advance for any pointers!
>
> Peter
>
> PS: I know my R is not the most up to date, but I haven't found
> anything about Date mentioned in the changelog for the 3.x series.
>
>
>> sessionInfo()
> R version 3.0.2 Patched (2013-10-08 r64039)
> Platform: x86_64-unknown-linux-gnu (64-bit)
>
> locale:
> [1] LC_CTYPE=en_US.utf8 LC_NUMERIC=C
> [3] LC_TIME=en_US.utf8 LC_COLLATE=en_US.utf8
> [5] LC_MONETARY=en_US.utf8 LC_MESSAGES=en_US.utf8
> [7] LC_PAPER=en_US.utf8 LC_NAME=C
> [9] LC_ADDRESS=C LC_TELEPHONE=C
> [11] LC_MEASUREMENT=en_US.utf8 LC_IDENTIFICATION=C
>
> attached base packages:
> [1] stats graphics grDevices utils datasets methods base