round.Date and trunc.Date not working / implemented

  > This is a workaround, and could be the basis for a round.Date
improvement:
  >?? date <- Sys.Date()
  >?? as.Date(round(as.POSIXct(date), "years"))
  >?? as.Date(round(as.POSIXct(Sys.Date() + 180), "years"))
  > Duncan Murdoch
That would work, perhaps structured similarly as `trunc.Date` is.
The only issue might be that `trunc.Date` is currently using `round.Date`
in its numeric form likely to prevent ?expensive? conversion to POSIXt
when it is not required.

  > trunc.Date
  > function (x, units = c("secs", "mins", "hours", "days", "months",
  >? ?? "years"), ...)
  > {
  >??? units <- match.arg(units)
  >??? if (units == "months" || units == "years")
  >??????? as.Date(trunc.POSIXt(x, units, ...))
  >??? else round(x - 0.4999999)
  > }
Perhaps the working version of `round.Date` could be:

  ? round.Date = function(x, units = c("secs", "mins", "hours", "days",
"months", "years")){
  ??? units = match.arg(units)

  ??? if (units == "months" || units == "years")
  ??? ? as.Date(round.POSIXt(x, units, ...))
  ??? else .Date(round(as.numeric(x)))
  ? }
If I were writing round.Date, I wouldn't offer the user an explicit 
option to round to seconds, minutes or hours.  So the header could be

     round.Date = function(x, units = c("days", "months", "years"))

Whether the function would complain if given other units like "secs" 
would need to be decided.

Like Henrik, I don't really like direct calls to methods such as your 
round.POSIXt call.  Those make assumptions that may not be true for 
weird corner cases where the class is not just "Date", but something 
more complicated that happens to have "Date" as one of the components of 
the class.  However, the related functions use that writing style, so I 
shouldn't complain too much.

Duncan Murdoch
Or perhaps `unclass` instead of `as.numeric`. Since the default `units`
for round(x) evaluates
to `sec`, this should correctly skip the first condition in `round` and
get to the correct numeric
rounding.

Perhaps the `trunc.Date` should be modified as well so that the call to
`round.Date` is skipped in favour of internal `round.numeric`, saving
few cycles.

-- Jirka

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round.Date and trunc.Date not working / implemented

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