Operation on vectors about lubridate HOT 5 CLOSED

(note: I'm moving the content of this comment into its own issue, because it seems related and significant, but not the issue discussed here) - 7/13/09

It seems more complicated than it initially appeared. A single duration is a 1 x 2 data frame. So c(dur, dur) returns a list of four numeric objects which we can't add and subtract as durations, while list(dur, dur) returns a list of two duration objects.

it is less obvious how to put durations into a data frame in a satisfactory manner. The best I've found is

> data.frame(cbind(c(a,a), c(a,a)))
X1   X2
1 1, 1 1, 1
2 1, 1 1, 1

which doesn't print the durations correctly, but is of class "data.frame"

from lubridate.

(I deleted two comments about R crashing, because I located the error to side effects of a length.duration() I had made (and now removed)) - 7/13/09

from lubridate.

THE ISSUE HERE
To have arguments of differing lengths, the durations/POSIXts/difftimes must be stored in a list or vector or data.frame. As the default, these data structures have the class "list" (or whichever is appropriate) but not the class attributes of their individual elements: "duration" "POSIXt" or "difftime."

Hence, R does not call '+.duration' when adding lists of durations. It is unclear what R does call as base::'+.list' and base::'+.default' do not exist. Either way when a list is involved in addition, R automatically returns Error: non-numeric argument to binary operators

Do we write a '+.list' to screen for durations? I think this depends also on our decision of which data structures to store durations in and how (see related issue)

from lubridate.

Duration is just a data frame, so the natural combining operation is rbind. Have a look at the code for c.duration,+ and print.duration for the basic idea.

from lubridate.

The ops functions work for vectors of different lengths. If the different lengths are not multiples of each other it provides a warning message just as base::r does. But I wonder why R doesn't use an error message instead...

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