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dmonths and dyears incorrectly defined #889

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jeffreyoldham opened this issue May 1, 2020 · 3 comments
Closed

dmonths and dyears incorrectly defined #889

jeffreyoldham opened this issue May 1, 2020 · 3 comments

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@jeffreyoldham
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@jeffreyoldham jeffreyoldham commented May 1, 2020

Adding dmonths and dyears to dates does not yield correct values because they are defined in terms of seconds. Furthermore, dmonths was added in 1.7.8 but not exported. To correct, durations must be reimplemented to account for irregular duration lengths.

  1. Adding dmonths or dyears to a date yield the wrong values.
  2. dmonths was not exported via NAMESPACE.
library(lubridate)
lubridate::dmonths
# Error: 'dmonths' is not an exported object from 'namespace:lubridate'

lubridate::ymd("1970-01-01") + lubridate::dyears ( 1 )
# wrong answer: [1] "1971-01-01 06:00:00 UTC"
# correct answer: [1] "1971-01-01 00:00:00 UTC"

The underlying problem is the duration of a month or a year depends on the particular month or year. 1972-02 has 29 days, while 1972-03 has 31. 1972 has 366 days, while 1973 has 365 days. Adding these durations to dates needs to reflect this. The duration object should be reimplemented to reflect this lack of regularity. (The absence of support for leap seconds also indicates the need for a fundamental reimplementation of durations.)

@vspinu vspinu closed this as completed in 8b5c838 May 2, 2020
@vspinu
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@vspinu vspinu commented May 2, 2020

You are right about dmonth not being exported.

Regarding your other problem, it's as expected. durations are fixed, and dmonth and dyear are average durations. This is documented.

What you need is a period.

> ymd("2020-01-01") + dyears(1)
[1] "2021-01-01"

@MokeEire
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@MokeEire MokeEire commented Jun 19, 2020

Why is this closed? dmonths() is still not exported.

@vspinu
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@vspinu vspinu commented Jun 19, 2020

it is in v1.7.9

lubridate::dmonths
function(x = 1) new("Duration", x * average_durations[["month"]])
<bytecode: 0x56471b490d78>
<environment: namespace:lubridate>

netbsd-srcmastr pushed a commit to NetBSD/pkgsrc that referenced this issue May 30, 2021
Version 1.7.10
==============

### NEW FEATURES

* `fast_strptime()` and `parse_date_time2()` now accept multiple formats and apply them in turn

### BUG FIXES

* [#926](tidyverse/lubridate#926) Fix incorrect division of intervals by months involving leap years
* Fix incorrect skipping of digits during parsing of the `%z` format

Version 1.7.9.2
===============

### NEW FEATURES

* [#914](tidyverse/lubridate#914) New `rollforward()` function
* [#928](tidyverse/lubridate#928) On startup lubridate now resets TZDIR to a proper directory when it is set to non-dir values like "internal" or "macOS" (a change introduced in R4.0.2)
* [#630](tidyverse/lubridate#630) New parsing functions `ym()` and `my()`

### BUG FIXES

* [#930](tidyverse/lubridate#930) `as.period()` on intervals now returns valid Periods with double fields (not integers)



Version 1.7.9
=============

### NEW FEATURES

* [#871](tidyverse/lubridate#893) Add `vctrs` support


### BUG FIXES

* [#890](tidyverse/lubridate#890) Correctly compute year in `quarter(..., with_year = TRUE)`
* [#893](tidyverse/lubridate#893) Fix incorrect parsing of abbreviated months in locales with trailing dot (regression in v1.7.8)
* [#886](tidyverse/lubridate#886) Fix `with_tz()` for POSIXlt objects
* [#887](tidyverse/lubridate#887) Error on invalid numeric input to `month()`
* [#889](tidyverse/lubridate#889) Export new dmonth function

Version 1.7.8
=============

### NEW FEATURES

* (breaking) Year and month durations now assume 365.25 days in a year consistently in conversion and constructors. Particularly `dyears(1) == years(1)` is now `TRUE`.
* Format and print methods for 0-length objects are more consistent.
* New duration constructor `dmonths()` to complement other duration constructors.
*
* `duration()` constructor now accepts `months` and `years` arguments.
* [#629](tidyverse/lubridate#629) Added `format_ISO8601()` methods.
* [#672](tidyverse/lubridate#672) Eliminate all partial argument matches
* [#674](tidyverse/lubridate#674) `as_date()` now ignores the `tz` argument
* [#675](tidyverse/lubridate#675) `force_tz()`, `with_tz()`, `tz<-` convert dates to date-times
* [#681](tidyverse/lubridate#681) New constants `NA_Date_` and `NA_POSIXct_` which parallel built-in primitive constants.
* [#681](tidyverse/lubridate#681) New constructors `Date()` and `POSIXct()` which parallel built-in primitive constructors.
* [#695](tidyverse/lubridate#695) Durations can now be compared with numeric vectors.
* [#707](tidyverse/lubridate#707) Constructors return 0-length inputs when called with no arguments
* [#713](tidyverse/lubridate#713) (breaking) `as_datetime()` always returns a `POSIXct()`
* [#717](tidyverse/lubridate#717) Common generics are now defined in `generics` dependency package.
* [#719](tidyverse/lubridate#719) Negative Durations are now displayed with leading `-`.
* [#829](tidyverse/lubridate#829) `%within%` throws more meaningful messages when applied on unsupported classes
* [#831](tidyverse/lubridate#831) Changing hour, minute or second of Date object now yields POSIXct.
* [#869](tidyverse/lubridate#869) Propagate NAs to all internal components of a Period object

### BUG FIXES

* [#682](tidyverse/lubridate#682) Fix quarter extraction with small `fiscal_start`s.
* [#703](tidyverse/lubridate#703) `leap_year()` works with objects supported by `year()`.
* [#778](tidyverse/lubridate#778) `duration()/period()/make_difftime()` work with repeated units
* `c.Period` concatenation doesn't fail with empty components.
* Honor `exact = TRUE` argument in `parse_date_time2`, which was so far ignored.

Version 1.7.4
=============

### NEW FEATURES

* [#658](tidyverse/lubridate#658) `%within%` now accepts a list of intervals, in which case an instant is checked if it occurs within any of the supplied intervals.

### CHANGES

* [#661](tidyverse/lubridate#661) Throw error on invalid multi-unit rounding.
* [#633](tidyverse/lubridate#633) `%%` on intervals relies on `%m+` arithmetic and doesn't produce NAs when intermediate computations result in non-existent dates.
* `tz()` always returns "UTC" when `tzone` attribute cannot be inferred.

### BUG FIXES

* [#664](tidyverse/lubridate#664) Fix lookup of period functions in `as.period`
* [#649](tidyverse/lubridate#664) Fix system timezone memoization

Version 1.7.3
=============

### BUG FIXES

* [#643](tidyverse/lubridate#643), [#640](tidyverse/lubridate#640), [#645](tidyverse/lubridate#645) Fix faulty caching of system timezone.
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