`duration` ignores class of first argument

[klmr]

See 🔗 Stack Overflow question.

In a nutshell, the following code

time = now()
five_sec = interval(time, time + 5)
duration(five_sec)
# [1] "5s"
duration(five_sec, units = 'days')
# [1] "432000s (~5 days)"

Yields an unexpected output for the last line because the class of five_sec is ignored, and its unit is overridden to be interpreted as days. This makes sense for a unitless num argument — but five_sec isn’t unitless by virtue of being an Interval.

The expected behaviour is that this should be disallowed — i.e. throw an error, or at least signal a stern warning that the interval’s unit is being ignored.

[Christoph999]

I thought the result is transferred to the specified unit. In the case above I would have expected 5/(24*3600). In case of years (which can have 365 or 366 days) this feature is really helpful.

[vspinu]

Yes. It should be disallowed. For conversion use as.duration.

[Christoph999]

Thank you. Perhaps you can add a comment somewhere that for conversion you
need
as.numeric(as.duration(i1), units = "days")
or
as.numeric(i1, units = 'days') # Throwing a message on my computer - I don't know the reason.

I could not find it in the descrition nor in the article "Dates and Times
Made Easy with lubridate"...

[vspinu]

Hm. I am starting thinking this was a mistake. There might be plenty of derived classes from numeric that are valid inputs into duration constructor. The fact that lubridate's interval and period inherit from numeric was a mistake. It might be changed some day.

I am replacing this change with a much weaker check for "Period" and "Interval" class.

[vspinu]

as.numeric(i1, units = 'days')# Throwing a message on my computer - I don't know the reason.

Not anymore in the development version of lubridate.