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Test DateIntervals[ ] starting in the InfinitePast?

Posted 11 months ago
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I have a DateInterval object that might begin in the InfinitePast and I want to test to see if this is the case. When you construct such a DateInterval it will have it's granularity updated to match the smallest granularity of the other end point. So for example DateInterval[{InfinitePast,Today}]["Min"] will give a DateObject with a year of -Infinity but it will also have day and month fields and a Day level granularity.

I first tried using DateOverlapsQ but that didn't work.

I also tried extracting the Year value to test to see if it's -Infinity but it seems to give an error (it used to work in 12.1, now under 12.2 it seems like it tests to see that the Year is an integer.)

I also tried to manually change the granularity of infinite past to match the interval granularity, but it seems like this doesn't work as, for example, DateObject[InfinitePast,"Day"] just keeps the same granularity of Eternity. This suggests that the granularity change on InfinitePast in the Min of the DateInterval is perhaps a bug? Maybe it should just return the regular InifnitePast DateObject, and then I could easily test it using regular equality.

3 Replies
Posted 11 months ago

Hi Nicholas,

Try MinDate

d = DateInterval[{InfinitePast, Today}]
min = MinDate[d, "Year"]

InputForm@min
(* DateObject[{-Infinity}, "Year", "Gregorian", -6.] *)

MinDate gives the same results as DateInterval["Min"], but what is the way to do the comparison? For example:

MinDate[DateInterval[{InfinitePast,Today}]]==InfinitePast

returns unevaluated. I would like to be able to test an arbitrary DateInterval to see if it starts in the InfinitePast

Posted 11 months ago

Ah, I misunderstood the question. How about

infinitePastQ[interval_DateInterval] := Not@FreeQ[interval, -Infinity]

infinitePastQ@DateInterval[{InfinitePast, Today}]
(* True *)

infinitePastQ@DateInterval[{InfinitePast, DateObject[{2021}]}]
(* True *)

infinitePastQ@DateInterval[{Today, InfiniteFuture}]
(* False *)

infinitePastQ@DateInterval[{InfinitePast, InfiniteFuture}]
(* True *)
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