[Rd] RFC: make as.difftime more consistent or convenient

S Ellison S@Elli@on @ending from LGCGroup@com
Fri Aug 3 16:23:11 CEST 2018

> Thank you for your comments! But, what you wrote is known. What do you
> want to express with regard to my questions?
> I wrote:
> > … there is no appropriate format ...,
> > although "weeks" is a legitimate unit of 'difftime':
> >
> >     > as.difftime("12 w", "%...")
> >
> >     > as.difftime("12 weeks")
> >     Time difference of 12 weeks
> >
> >     1. What do you think about making the behavior of 'as.difftime' more
> >   consistent by accepting also formats for "days" and "weeks"?

as.difftime calls strptime to apply the format argument.

If I  wanted to extend the range of formats as.difftime accepts, I'd leave as.difftime alone and look at how strptime could be extended to cover the formats you envisage.

But... I wouldn’t do that either. strptime is essentially a call to an .Internal function and very likely reliant on established  C code for the already very flexible standard C function strptime, which strptime clearly mirrors intentionally. That usually makes things dangerous to tinker with in the short term and hard to maintain in the long term.

So  if you want to do something that will readily convert all combinations of things like '12 w', '12W', '12wks', '3m 2d', 1wk 2d', '18d' etc, write that as a stand-alone routine that converts those 'simple' formats directly to difftime objects and call it something like 'strpdifftime', which would allow it to be added (if it's wanted a lot) with minimal impact to existing code.

S Ellison

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