[C++] Implement floor/ceil/round for temporal objects

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This would enable us to implement the linked R ticket

Reporter: Nicola Crane / @thisisnic
Assignee: Rok Mihevc / @rok
Watchers: Rok Mihevc / @rok

Related issues:

• [R] Implement bindings for lubridate's floor_date, ceiling_date, and round_date (is required by)

PRs and other links:

• GitHub Pull Request #11818

_{Note: This issue was originally created as ARROW-14822. Please see the migration documentation for further details.}

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Antoine Pitrou / @pitrou:
Hmm... what are the desired semantics here?

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Nicola Crane / @thisisnic:
Actually; this might be a bit different to just extending floor/ceiling/round - we want to be able to support the lubridate functions here: https://lubridate.tidyverse.org/reference/round_date.html

We basically would like to be able to round a date, specifying which component to round it to (in lubridate valid value for unit are second, minute, hour, day, week, month, bimonth, quarter, season, halfyear and year), and account for the additional complication of specifying the day on which the week starts when rounding by week.

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Antoine Pitrou / @pitrou:
cc @lidavidm

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David Li / @lidavidm:
It appears pandas has a similar operation: https://pandas.pydata.org/docs/reference/api/pandas.Series.dt.round.html which also has options for handling ambiguous/nonexistent dates. Neither allow you to control the rounding mode (and it is not specified for Pandas). Postgres only implements truncation: https://www.postgresql.org/docs/14/functions-datetime.html#FUNCTIONS-DATETIME-TRUNC

 

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Rok Mihevc / @rok:
@lidavidm I'm thinking to pick this up. Anything I take into account?

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David Li / @lidavidm:
@rok I don't think there's anything in particular. There's just quite a range of options to account for (Pandas has the ambiguous/nonexistent timestamp options, but only implements rounding; R implements truncate/round/ceiling and lets you control the start-of-week).

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Joris Van den Bossche / @jorisvandenbossche:

It appears pandas has a similar operation: https://pandas.pydata.org/docs/reference/api/pandas.Series.dt.round.html which also has options for handling ambiguous/nonexistent dates. Neither allow you to control the rounding mode (and it is not specified for Pandas).

Pandas has separate ceil and floor methods for timestamps as well for different rounding modes (but it's true that round doesn't really specify how it is rounding)

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Rok Mihevc / @rok:
@jorisvandenbossche I plan to make separate kernels for round/floor/ceil.
It appears rounding in pandas (and I suspect in lubridate) is done to time intervals, which seems fine for intervals of day and smaller. However it would be nice to round to week/month/etc where the result would be "calendar rounded" instead of "interval rounded". So I'm trying to set that up, please stop me if you disagree.

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Joris Van den Bossche / @jorisvandenbossche:
Pandas indeed only implements rounding to "fixed size" frequencies/intervals (so day or less). But I think that's more a practical reason that this is not supported (easier to implement). But so I think it is fine to add in Arrow if we have the utilities for that (through date.h)

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David Li / @lidavidm:
Issue resolved by pull request 11818
#11818