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as.Date woes

2 messages · Peter Langfelder

Peter Langfelder
# 
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:
[1] "2012-04-30"
[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:
[1] "2014-08-20"   #### Correct
[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??
[1] 16302
[1] 16302
[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.
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
Peter Langfelder
# 
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: