Rounding datetime objects to a given granularity

Question

How does one round datetime objects to any granularity (eg "Hour","Minute" etc)?

What I'm looking for is a function that would do the following:

DateRound[DateObject[{2018, 7, 7, 10, 55, 42.}], "Hour"]

-> DateObject[{2018, 7, 7, 11, 0, 0.}]

DateRound[DateObject[{2018, 7, 7, 10, 55, 42.}], "Minute"]

-> DateObject[{2018, 7, 7, 10, 56, 0.}]

That is, round the given DateObject to whatever granularity is given - the nearest minute, nearest hour, day, month etc.

I can Floor dates using CurrentDate:

CurrentDate[DateObject[{2018, 7, 7, 10, 55, 42.}], "Hour"]

-> DateObject[{2018, 7, 7, 10}]

or by using DateValue:

DateValue[DateObject[{2018, 7, 7, 10, 55, 42.}], {"Year", "Month", "Day", "Hour"}]

-> {2018, 7, 7, 10}

but as you can see, this does not give me the rounded granularity (11), but the floored granularity (10).

I know about DayRound, which is approximately the functionality I'm looking for, but it doesn't support any time operations.

Answer 1

Assuming DatePlus handles adding fractional units properly (which I'm pretty sure it does), I would try adding half the unit you want and then doing the floor operation that CurrentDate does. It works for your examples.

dateRound[d_, s_] := CurrentDate[DatePlus[d, {.5, s}], s]