Date Computations

[paulmansour]

Say you were introducing a new programmer to Dyalog APL. Say he wanted to compute the days difference between two dates, or do various date arithmetic, adding days to a date, etc.

Would you suggest he roll his own functions? Would you point him to a Dyalog library or workspace? Which one? Or to an external library in R or Python?

[Veli-Matti]

..eh:
#.DateToIDN
#.IDNToDate
-wm

[Phil Last]

..eh:
#.DateToIDN
#.IDNToDate
-wm

work on only a single date so require "each" on what is an obvious array problem.
I'm not suggesting mine are perticularly quick but the same operation using APL on ten thousand dates is seven times as quick.

[Vince|Dyalog]

When using DateToIDN and IDNToDate, it is worth remembering that these methods are only exposed if root properties are exposed:

Why can't I see Root Methods such as #.DateToIDN?
http://www.dyalog.com/forum/viewtopic.php?f=22&t=161

Or, you can always call these methods like this:

      +2 ⎕nq '.' 'datetoidn' 2018 1 18
43117

Regards,

Vince

[paulmansour]

Let's add time to the problem. Say I want to compute the number of seconds elapsed between two time stamps.

My guess is there is no date library, or workspace with an extensive collection of date/time functions. Would that be correct?

[PGilbert]

With using .Net I have contributed this to the AplWiki: https://aplwiki.com/netDateTime

[Vince|Dyalog]

Hi Paul,

There is also the dfns.dws days and date dfns.

days ⍝ Day number from ⎕TS format.
date ⍝ ⎕TS format from day number.

      ⎕ts
2018 1 18 15 41 4 634
      days ⎕ts
43117.65355


      ⎕ts
2018 1 18 15 41 10 729
      days ⎕ts
43117.65361

Regards,

Vince

[Morten|Dyalog]

My guess is there is no date library, or workspace with an extensive collection of date/time functions. Would that be correct?

That is correct, and it is something we are working on. We've started a project based on the code which is shipped with MiServer https://github.com/Dyalog/MiServer/blob/master/Utils/dates.dyalog but this is somewhat oriented towards the needs of a web application. We would be very happy to receive both code contributions and suggestions for functions which should be in a complete date library.

Our intention is to make libraries of functions for date and string manipulation available on GitHub. Once we have a complete set of functions, we can talk about which parts of it (for example parsing and formatting) which we might want to rewrite in C and include in the interpreter as system functions or similar, for performance reasons.

[kai]

https://aplwiki.com/DateAndTime

(sometimes I feel tired)

[paulmansour]

Kai, do you know if anyone uses this library/class?