Changelog • lubridate

Version 1.9.4

CRAN release: 2024-12-08

Changes

Don’t use CET and EST as timezones to accommodate the upgrade of tzdata in the R-devel

Version 1.9.3

CRAN release: 2023-09-27

NEW FEATURES

#682 Add type=“year_start/end” argument to quarter() which produces a complete description of the quarter.

BUG FIXES

#1109 Fix recycling of the year slot in as.period(unit = "month") with Periods and Intervals.
#1133 Don’t error on addition on infinite periods.

Version 1.9.2

CRAN release: 2023-02-10

BUG FIXES

#1104 Fix incorrect parsing of months when %a format is present.

OTHER

Adapt to internal name changes in R-devel

Version 1.9.1

CRAN release: 2023-01-24

NEW FEATURES

as_datetime() accepts multiple formats in format argument, just like as_date() does.

BUG FIXES

#1091 Fix formatting of numeric inputs to parse_date_time.
#1092 Fix regression in ymd_hm on locales where p format is not defined.
#1097 Fix as_date("character") to work correctly with formats that include extra characters.
#1098 Roll over the month boundary in make_dateime() when units exceed their maximal values.
#1090 timechange has been moved from Depends to Imports.

Version 1.9.0

CRAN release: 2022-11-06

NEW FEATURES

roll argument to updating and time-zone manipulation functions is deprecated in favor of a new roll_dst parameter.
#1042 as_date with character inputs accepts multiple formats in format argument. When format is supplied, the input string is parsed with parse_date_time instead of the old strptime.
#1055 Implement as.integer method for Duration, Period and Interval classes.
#1061 Make year<-, month<- etc. accessors truly generic. In order to make them work with arbitrary class XYZ, it’s enough to define a reclass_date.XYZ method.
#1061 Add support for year<-, month<- etc. accessors for data.table’s IDate and ITime objects.
#1017 week_start argument in all lubridate functions now accepts full and abbreviated names of the days of the week.
The assignment value wday<- can be a string either in English or as provided by the current locale.
Date rounding functions accept a date-time unit argument for rounding to a vector of date-times.
#1005 as.duration now allows for full roundtrip duration -> as.character -> as.duration
#911 C parsers treat multiple spaces as one (just like strptime does)
stamp gained new argument exact=FALSE to indicate whether orders argument is an exact strptime formats string or not.
#1001 Add %within method with signature (Interval, list), which was documented but not implemented.
#941 format_ISO8601() gained a new option usetz="Z" to format time zones with a “Z” and convert the time to the UTC time zone.
#931 Usage of Period objects in rounding functions is explicitly documented.

BUG FIXES

#1036 %within% now correctly works with flipped intervals
#1085 as_datetime() now preserves the time zone of the POSIXt input.
#1072 Names are now handled correctly when combining multiple Period or Interval objects.
#1003 Correctly handle r and R formats in locales which have no p format
#1074 Fix concatenation of named Period, Interval and Duration vectors.
#1044 POSIXlt results returned by fast_strptime() and parse_date_time2() now have a recycled isdst field.
#1069 Internal code handling the addition of period months and years no longer generates partially recycled POSIXlt objects.
Fix rounding of POSIXlt objects
#1007 Internal lubridate formats are no longer propagated to stamp formater.
train argument in parse_date_time now takes effect. It was previously ignored.
#1004 Fix c.POSIXct and c.Date on empty single POSIXct and Date vectors.
#1013 Fix c(POSIXct,POSIXlt) heterogeneous concatenation.
#1002 Parsing only with format j now works on numeric inputs.
stamp() now correctly errors when no formats could be guessed.
Updating a date with timezone (e.g. tzs = "UTC") now returns a POSIXct.

INTERNALS

lubridate is now relying on timechange package for update and time-zone computation. Google’s CCTZ code is no longer part of the package.
lubridate’s updating logic is now built on top of timechange package.
Change implementation of c.Period, c.Duration and c.Interval from S4 to S3.

Version 1.8.0

CRAN release: 2021-10-07

NEW FEATURES

#960 c.POSIXct and c.Date can deal with heterogeneous object types (e.g c(date, datetime) works as expected)

BUG FIXES

#994 Subtracting two duration or two period objects no longer results in an ambiguous dispatch note.
c.Date and c.POSIXct correctly deal with empty vectors.
as_datetime(date, tz=XYZ) returns the date-time object with HMS set to 00:00:00 in the corresponding tz

CHANGES

#966 Lubridate is now built with cpp11 (contribution of @DavisVaughan)

Version 1.7.10

CRAN release: 2021-02-26

NEW FEATURES

#955 Add type argument to quarter() for more control over the returned class
fast_strptime() and parse_date_time2() now accept multiple formats and apply them in turn

BUG FIXES

#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

CRAN release: 2020-11-13

NEW FEATURES

#914 New rollforward() function
#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 New parsing functions ym() and my()

BUG FIXES

#930 as.period() on intervals now returns valid Periods with double fields (not integers)

Version 1.7.9

CRAN release: 2020-06-08

NEW FEATURES

#871 Add vctrs support

BUG FIXES

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

Version 1.7.8

CRAN release: 2020-04-06

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 Added format_ISO8601() methods.
#672 Eliminate all partial argument matches
#674 as_date() now ignores the tz argument
#675 force_tz(), with_tz(), tz<- convert dates to date-times
#681 New constants NA_Date_ and NA_POSIXct_ which parallel built-in primitive constants.
#681 New constructors Date() and POSIXct() which parallel built-in primitive constructors.
#695 Durations can now be compared with numeric vectors.
#707 Constructors return 0-length inputs when called with no arguments
#713 (breaking) as_datetime() always returns a POSIXct()
#717 Common generics are now defined in generics dependency package.
#719 Negative Durations are now displayed with leading -.
#829 %within% throws more meaningful messages when applied on unsupported classes
#831 Changing hour, minute or second of Date object now yields POSIXct.
#869 Propagate NAs to all internal components of a Period object

BUG FIXES

#682 Fix quarter extraction with small fiscal_starts.
#703 leap_year() works with objects supported by year().
#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

CRAN release: 2018-04-11

NEW FEATURES

#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 Throw error on invalid multi-unit rounding.
#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 Fix lookup of period functions in as.period
#649 Fix system timezone memoization

Version 1.7.3

CRAN release: 2018-02-27

BUG FIXES

#643, #640, #645 Fix faulty caching of system timezone.

Version 1.7.2

CRAN release: 2018-02-06

NEW FEATURES

Durations, Periods and difftimes are now comparable with each other.
interval constructor accepts start and end character vectors in ISO 8601 format
#362 Add support for ISO 8601 formats in interval constructor
#622 Add support for ISO 8601 formats in periods and durations constructor

CHANGES

Correct license to the originally intended GPL (>= 2)

BUG FIXES

#605 Fix wrong ceiling of days during DST transition.
#607 Re-instate format argument to as_date and as_datetime (regression in v1.7.1)
Fix intersection of intervals with missing values.
Fix UBSAN errors in update.cpp

Version 1.7.1

CRAN release: 2017-11-03

BUG FIXES

#575, #600, #602 Fix zoneinfo lookup on windows and solaris.
#598 Fix broken parsing of ymd_hms strings by as_date.
#597 Fix broken parsing of ymd strings by as_datetime.

Version 1.7.0

CRAN release: 2017-10-29

NEW FEATURES

Reduced memory footprint on trunc_multi_unit so that it overwrites the vector argument x versus making a new vector y.
#438 New function force_tzs for “enforcement” of heterogeneous time zones.
#438 New function local_time for the retrieval of local day time in different time zones.
#560 New argument cutoff_2000 for parsing functions to indicate 20th century cutoff for y format.
#257 New week_start parameter in wday and wday<- to set week start.
#401 New parameter locale in wday. Labels of the returned factors (when label=TRUE) now respect current locale.
#485 quarter gained a new argument fiscal_start to address the issue of different fiscal conventions.
#492 New functions epiweek and epiyear.
#508 New parameter locale in month. Labels of the returned factors (when label=TRUE) now respect current locale.
#509 New parameter week_start to floor_date, ceiling_date and round_date.
#519 Support fractional units in duration and period string constructors.
#502 Support rounding to fractions of a seconds.
#529 Internal parser now ignores the case of alpha months (B format)
#535 Rounding to season is now supported.
#536 as_date and as_datetime now understand character vectors.
New parsing parameters to parse_date_time - train=TRUE and drop=FALSE which allow more refined control of the format guessing. Formats are no longer dropped in the process by default, process which resulted in surprising behavior on several occasions (#516,#308,#307).

CHANGES

#401 [Breaking Change] Labels returned by wday and month are now in current locale. The abbreviated labels in English locales have been changed to standard abbreviations (Tues -> Tue, Thurs -> Thu etc.).
#469 Throw warning in with_tz on invalid timezone.
#572 B and b formats no longer match numeric months. This corresponds to the original intent, and was always documented as such.

BUG FIXES

#314, #407, #499 Make days, dhours, round_date work when the methods package is not loaded.
#543 Make wday work on character inputs as it is the case with all other day accessors.
#566 Comparing durations and periods no-longer inf-loops.
#556 Fix incorrect scoring of y format when it’s the last in format order (as in mdy).
#584 Fix interval by period division.
#559 Parsing of alpha-months in English locales now drops correctly to low level C parsing. Thus, parsing with multiple orders containing m and b formats now works correctly.
#570, #574 Fix broken date() when called with missing argument.
#567 Fix year update and rounding for leap years.
#545 Fix wrong locale selection in stamp.
#466 Fix wrong formats within ymd_h family of functions.
#472 Printing method for duration doesn’t throw format error on fractional seconds.
#475 character<> comparisons is no longer slow.
#483 Fix add_duration_to_date error when duration first element is NA.
#486 ceiling_date handles NA properly.
#491 make_datetime respects tz argument and is much faster now.
#507 Period and duration parsers now understand 0 units.
#524 Correctly compute length of period in months (issue #490)
#525 Fix to prevent day<-, minute<-, etc. from producing an error when length(x) is 0 (issue #517)
#530 parse_date_time now throw warnings only for actual parsing errors (input with all NAs are silent)
#534 Fix arithmetic with large numbers
#554 Fix tests when running in non-English locales

Version 1.6.0

CRAN release: 2016-09-13

NEW FEATURES

#464 New function semester to extract semesters form date-time objects.
#459 Flexible C-level parsing for periods and durations has been implemented; period and duration constructors now accept string as first argument. Same parsing rules apply to the ‘unit’ parameter in rounding functions.
#459 Comparison between character vectors and periods/durations is now possible.
#287 C-level and derivative parsers now handle English months (%b and %B formats) irrespective of the current locale.
#327 C-level and derivative parsers now handles English AM/PM indicator irrespective of the current locale.
#417 hms, hm, ms gained new argument roll=TRUE which rolls minutes and seconds bigger than 59 towards higher units.
#445 Division of intervals by periods is now accurate.
#442 round_date, floor_date and ceiling_date now support rounding to multiple of units.
#422 New parsing function yq for parsing most common version of quarter strings.
#422 New format q for parsing quarters in all lubridate parsing functions.
#441 Comparison between POSIXt and Date objects is now possible.
#437 New function as_datetime to coerce to POSIXct object. A counterpart of as_date.
#412 New function make_date to produce Date objects. A counterpart of make_datetime.
#443 Behavior of ceiling_date for Date objects was changed to what most of the users expect. Rounding up by months now produces first day of the next months even for first day of the month.
#268 round_date, ceiling_date, and floor_date now accept “quarter”, “bimonth”, and “halfyear” as unit options.
#418 C level parsing functions understand 24:00:00 in datetime strings.

CHANGES

Low letter specs for HMS (hms,hm,ms) in parse_date_time and related functions are now deprecated.
#445 No more warning on occasional imprecise period length conversions. Imprecise arithmetic with periods is extensively documented.
pretty.* family of functions were renamed and are no longer exported. If you need to use them, use lubridate:::pretty_* versions.
change_on_boundary argument in ceiling_date does not allow for global option anymore.
as.duration, as.numeric don’t show “only estimate” messages on conversion from periods. The occasional approximate conversion is documented and deemed common knowledge.
as.numeric with unit="month" now works on duration objects.
#403 Update on Date objects now return POSIXct instead of POSIXlt.
#411 format mdy or myd beginning with "January" or "Jan" now parsing correctly
here and olson_time_zones were deprecated in favor of new and base OlsonNames respectively.
Internally, S4 Compare and Ops generics were cleaned and simplified.
#456 Evaluation output in documentation examples was removed.

BUG FIXES

#479 Fix the inconsistent behavior in ceiling_date when unit = "week"
#463 Fix NA subscripting error in %m+% when rollback is involved.
#462 Non-numeric or non-character arguments are disallowed as arguments to period and duration constructors.
#458 When year is missing in parsing, return consistently year 0.
#448 Correctly handle missing months and days in C parser.
#450 Fix incorrect handling of DST gaps in date_decimal and decimal_date.
#420 as.numeric correctly converts periods to (approximate) numeric time lengths.

Version 1.5.6

CRAN release: 2016-04-06

NEW FEATURES

#390 ceiling_date gains new argument change_on_boundary to allow ceiling on boundary of date-time objects.
C parser can now produce a list of date-time components suitable for POSIXlt constructors.
parse_date_time2 and fast_strptime gain new lt argument to control type of output.
#373 New date and date<- additions to the year, month etc family of accessors.
#365 New very fast datetime constructor make_datetime (dropin replacement of ISOdatetime).
#344 force_tz and with_tz can handle data.frames component-wise.
#355 New as_date replacement of as.Date with more intuitive behavior with non-UTC timezones.
#333 hms parsers now handle negative components.

CHANGES

#391 ymd family of functions return Date object when tz argument is NULL (new default) and POSIXct otherwise.
#364 Remove epoch functions.
For consistency with base:strptime fast_strptime now returns POSIXlt object. That is, its lt argument defaults to TRUE.

BUG FIXES

interval constructor treats timezones correctly and works with UTC whenever meaningful.
#371 as.period correctly computes months with intervals spanning multiple years.
#388 time_length and add_with_rollback now work correctly with missing intervals.
#394 fast_strptime and parse_date_time2 correctly treat non-UTC time zones.
#399 floor_date and round_date are not preserving tz component for larger than day units

Version 1.5.0

CRAN release: 2015-12-03

NEW FEATURES

New time_length method.
Added isoyear function to line up with isoweek.
#326 Added exact = TRUE option to parse_date_time for faster and much more flexible specification of formats.
New simple argument to fit_to_timeline and update methods mostly intended for internal use.
#315 Implement unique method for interval class.
#295 New args preserve_hms and roll_to_first in rollback function.
#303 New quarter option in floor_date and friends.
#348 New as.list.Interval S3 method.
#278 Added settors and accessors for qday (quarter day).

CHANGES

New maintainer Vitalie Spinu (@vspinu)
Time span constructors were re-factored; new_interval, new_period, new_duration, new_difftime were deprecated in favor of the more powerful interval, period, duration and make_difftime functions.
eseconds, eminutes etc. were deprecated in favor of dsecons, dminutes etc.
Many documentation improvements.
New testthat conventions are adopted. Tests are now in test/testthat.
Internally isodate was replaced with a much faster parse_date_time2(paste(...)) alternative
#325 Lubridate’s trunc, ceiling and floor functions have been optimized and now are relying on R’s trunc.POSIXct whenever possible.
#285 Algebraic computations with negative periods are behaving asymmetrically with respect to their positive counterparts.
Made necessary changes to accommodate new zoo-based fst objects.

BUG FIXES

#360 Fix c parser for Z (zulu) indicator.
#322 Explicitly encode formatted string with enc2utf8.
#302 Allow parsing long numbers such as 20140911000000 as date+time.
#349 Fix broken interval -> period conversion.
#336 Fix broken interval-> period conversion with negative diffs.
#227 Treat “days” and “years” units specially for pretty.point.
#286 %m+-% correctly handles dHMS period components.
#323 Implement coercion methods for Duration class.
#226 Propagate NAs in int_standardize
#235 Fix integer division with months and years.
#240 Make ceiling_date skip day light gap.
#254 Don’t preprocess a/A formats if expressly specified by the user.
#289 Check for valid day-months combinations in C parser.
#306 When needed double guess with preproc_wday=T.
#308 Document sparse format guessing in parse_date_time.
#313 Fixed and optimized fit_to_timeline function.
#311 Always use UTC in isoweek computation
#294 Don’t use years in seconds_to_period.
Values on $<- assignment for periods are now properly recycled.
Correctly handle NA subscripting in round_date.

Version 1.4.0

CHANGES

#219 In interval use UTC when tzone is missing.
#255 Parse yy > 68 as 19yy to comply with strptime.

BUG FIXES

#266 Include time-zones.R in coercion.R.
#251 Correct computation of weeks.
#262 Document that month boundary is the first second of the month.
#270 Add check for empty unit names in standardise_lt_names.
#276 Perform conversion in as.period.period if unit != NULL.
#284 Compute periods in as.period.interval without recurring to modulo arithmetic.
#272 Update examples for hms, hm and ms for new printing style.
#236 Don’t allow zeros in month and day during parsing.
#247 Uninitialized index was mistakenly used in subseting.
#229 guess_formats now matches flex regexp first.
dmilliseconds now correctly returns a Duration object.
Fixed setdiff for discontinuous intervals.

Version 1.3.3

CRAN release: 2013-12-31

CHANGES

New low level C parser for numeric formats and two new front-end R functions parse_date_time2 and fast_strptime. The achieved speed up is 50-100x as compared to standard as.POSIXct and strptime functions.

The user level parser functions of ymd_hms family drop to these C routines whenever plain numeric formats are detected.

BUG FIXES

olson_time_zones now supports Solaris OS
infinite recursion on parsing non-existing leap times was fixed

Version 1.3.2

CRAN release: 2013-12-05

Lubridate’s s4 methods no longer use the representation argument, which has been deprecated in R 3.0.0 (see ?setClass). As a result, lubridate is no longer backwards compatible with R <3.0.0.

Version 1.3.0

CRAN release: 2013-09-20

CHANGES

v1.3.0. treats math with month and year Periods more consistently. If adding or subtracting n months would result in a non-existent date, lubridate will return an NA instead of a day in the following month or year. For example, ymd("2013-01-31") + months(1) will return NA instead of 2013-03-04 as in v1.2.0. ymd("2012-02-29") + years(1) will also return an NA. This rule change helps ensure that date + timespan - timespan = date (or NA). If you’d prefer that such arithmetic just returns the last day of the resulting month, see %m+% and %m-%.
update.POSIXct and update.POSIXlt have been rewritten to be 7x faster than their versions in v1.2.0. The speed gain is felt in force_tz, with_tz, floor_date, ceiling_date, second<-, minute<-, hour<-, day<-, month<-, year<-, and other functions that rely on update (such as math with Periods).
lubridate includes a Korean translation provided by http://korea.gnu.org/gnustats/

NEW FEATURES

lubridate parser and stamp functions now handle ISO8601 date format (e.g., 2013-01-24 19:39:07.880-06:00, 2013-01-24 19:39:07.880Z)
lubridate v1.3.0 comes with a new R vignette. see browseVignettes("lubridate") to view it.
The accessors second, minute, hour, day, month, year and the settors second<-, minute<-, hour<-, day<-, month<-, year<- now work on Period class objects
users can control which messages lubridate returns when parsing and estimating with the global option lubridate.verbose. Run options(lubridate.verbose = TRUE) to turn parsing messages on. Run options(lubridate.verbose = FALSE) to turn estimation and coercion messages off.
lubridate parser functions now propagate NA’s just as as.POSIXct, strptime and other functions do. Previously lubridate’s parse functions would only return an error.
added [[ and [[<- methods for INterval, Period and Duration class objects
added %m+% and %m-% methods for Interval and Duration class objects that throw useful errors.
olson_time_zones retrieves a character vector is Olson-style time zone names to use in lubridate
summary methods for Interval, Period, and Duration classes
date_decimal converts a date written as a decimal of a year into a POSIXct date-time

BUG FIXES

fixed bug in way update.POSIXct and update.POSIXlt handle dates that occur in the fall daylight savings overlap. update will choose the date-time closest to the original date time (on the timeline) when two identical clock times exist due to the DST overlap.
fixed bugs that created unintuitive results for as.interval, int_overlaps, %within% and the interval methods of c, intersect, union, setdiff, and summary.
parse functions, as.interval, as.period and as.duration now handle vectors of NA’s without returning errors.
parsers better handle vectors of input that have more than 100 elements and many NAs
data frames that contain timespan objects containing NAs no longer fail to print
round_date, ceiling_date and update now correctly handle input of length zero
decimal_date no longer returns NaN for first second of the year

Version 1.2.0

CRAN release: 2012-10-04

CHANGES

lubridate 1.2.0 is significantly faster than lubridate 1.1.0. This is largely thanks to a parser rewrite submitted by Vitalie Spinu. Thank you, Vitalie. Some metrics:
- parser speed up - 60x faster
- with_tz speed up - 15x faster
- force_tz speed up - 3x faster
Development for 1.2.0 has also focused on improving the way we work with months. rollback rolls dates back to the last day of the previous month. provides more options for working with months. days_in_month finds the number of days in a date’s month. And, %m+% and %m-% provide a new way to ### handle unequal month lengths while doing arithmetic. See NEW FEATURES for more details
date parsing can now parse multiple date formats within the same vector of date-times. Parsing can also recognize a greater variety of date-time formats as well as incomplete (truncated) date-times. Contributed by Vitalie Spinu. Thank you, Vitalie.
1.2.0 introduces a new display format for periods. The display is more math and international friendly.
1.2.0 transforms negative intervals into periods much more gracefully (e.g, - 3 days instead of -1 years, 11 months, and 27 days)
S3 update methods are now exported

NEW FEATURES

stamp allows users to print dates in whatever form they like. Contributed by Vitalie Spinu. Thank you, Vitalie.
periods now handle fractional seconds. Contributed by Vitalie Spinu. Thank you, Vitalie.
date parsing can now parse multiple date formats within the same vector of date-times. Parsing can also recognize a greater variety of date-time formats as well as incomplete (truncated) date-times. Contributed by Vitalie Spinu. Thank you, Vitalie.
sort, order, rank and xtfrm now work with periods
as.period.Interval accepts a unit argument. as.period will convert intervals into periods no larger than the supplied unit.
days_in_month takes a date, returns the number of days in the date’s month. Contributed by Richard Cotton. Thank you, Richard.
%m+% and %m-% perform addition and subtraction with months (and years) without rollover at the end of a month. These can be used in place of + and -. These can’t be used with periods smaller than a month, which should be handled separately. An example of the new behavior:

ymd(“2010-01-31”) %m+% months(1) # “2010-02-28 UTC”

ymd(“2010-01-31”) + months(1) # “2010-03-03 UTC”

ymd(“2010-03-31”) %m-% months(1) # “2010-02-28 UTC”

ymd(“2010-01-31”) - months(1) # “2010-03-03 UTC”
rollback rolls a date back to the last day of the previous month.
quarter returns the fiscal quarter that a date occurs in. Like quartes in base R, but returns a numeric instead of a character string.

BUG FIXES

date parsers now handle NAs
periods now handle NAs
[<- now correctly updates all elements of a period inside a vector, list, or data.frame
period() now works with unit = “weeks”
ceiling_date no longer rounds up if a date is already at a ceiling
the redundant (i.e, repeated) hour of fall daylight savings time now displays with the correct time zone
update.POSIXct and update.POSIXlt handle vectors that sum to zero in the days argument
the format method for periods, intervals and duration now accurately displays objects of length 0.

Version 1.1.0

CRAN release: 2012-03-05

CHANGES

lubridate no longer overwrites base R methods for +, - , *, /, %%, and %/%. To recreate the previous experience of subtracting two date times to create an interval, we’ve added the interval creation function %–%.
lubridate has moved to an S4 object system. Timespans, Intervals, Durations, and Periods have each been redefined as an S4 class with its own methods.
arithmetic operations will no longer perform implicit class changes between timespans. Users must explicitly state how and when they wish class changes to occur with as.period(), as.duration(), and as.interval(). This makes code written with lubridate more robust, as such implicit changes often did not produce consistent behavior across a variety of operations. It also allows lubridate to be less chatty with fewer console messages. lubridate does not need to explain what it is doing, because it no longer attempts to do things whose outcome would not be clear. On the other hand, arithmetic between multiple time classes will produce informative error messages.
the internal structure of lubridate R code has been reorganized at https://github.com/tidyverse/lubridate to make lubridate more development friendly.

NEW FEATURES

intervals are now more useful and lubridate has more ways to manipulate them. Intervals can be created with %–%; modified with int_shift(), int_flip(), and int_standardize(); manipulated with intersect(), union(), and setdiff(); and used in logical tests with int_aligns(), int_overlaps(), and %within%. lubridate will no longer perform arithmetic between two intervals because the correct results of such operations is no more obvious than the correct result of adding two dates. Instead users are encouraged to use the new set operations or to directly modify intervals with int_start() and int_end(), which can also be used as settors. lubridate now supports negative intervals as well as positive intervals. Intervals also now display with a time zone.
Modulo methods for timespans have been changed to return a timespan. this allows modulo methods to be used with integer division in an intuitive manner, e.g. a = a %/% b * b + a %% b

Users can still achieve a numerical result by using as.numeric() on input before performing modulo.

Periods, durations, and intervals can now all be put into a data frame.
Periods, durations, and intervals can be intuitively subset with $ and []. These operations also can be used as settors with <-.
The parsing functions and the as.period method for intervals are now slightly faster.
month<- and wday<- settors accept names as well as numbers
parsing functions now have a quiet argument to parse without messages and a tz argument to directly parse times into the desired time zone.
logical comparison methods now work for period objects.

Version 0.2.6

CRAN release: 2012-01-10

use test_package to avoid incompatibility with current version of testthat
other minor fixes to pass R CMD check

Version 0.2.5

CRAN release: 2011-05-12

added ymdThms() for parsing ISO 8061 formatted combined dates and times

BUG FIXES

removed bug in parsing dates with “T” in them
modified as.period.interval() to display periods in positive units

Version 0.2.4

CRAN release: 2011-04-05

Add citations to JSS article

Version 0.2.3

CRAN release: 2010-12-09

NEW FEATURES

ymd_hms(), hms(), and ms() functions can now parse dates that include decimal values in the seconds element.
milliseconds(), microseconds(), nanoseconds(), and picoseconds() create period objects of the specified lengths. dmilliseconds(), dmicroseconds(), dnanoseconds(), and dpicoseconds() make duration objects of the specified lengths.

BUG FIXES

lubridate no longer overwrites months(), start(), and end() from base R. Start and end have been replaced with int_start() and int_end().
lubridate imports plyr and stringr packages, instead of depending on them.

Version 0.2.2

CRAN release: 2010-11-17

NEW FEATURES

made division, modulo, and integer division operations compatible with difftimes
created c() methods for periods and durations

BUG FIXES

fixed bug in division, modulo, and integer operations with timespans

Version 0.2.1

CRAN release: 2010-11-03

NEW FEATURES

created parsing functions ymd_hm ymd_h dmy_hms dmy_hm dmy_h mdy_hms mdy_hm mdy_h ydm_hms ydm_hm ydm_h, which operate in the same way as ymd_hms().

BUG FIXES

fixed bug in add_dates(). duration objects can now be successfully added to numeric objects.

Version 0.2

CRAN release: 2010-10-26

NEW FEATURES

division between timespans: each timespan class (durations, periods, intervals) can be divided by other timespans. For example, how many weeks are there between Halloween and Christmas?: (christmas - halloween) / weeks(1)
modulo operations between timespans
duration objects now have their own class and display format separate from difftimes
interval objects now use an improved data structure and have a cleaner display format
lubridate now loads its own namespace
math operations now automatically coerce interval objects to duration objects. Allows intervals to be used “right out of the box” without error messages.
created start() and end() functions for accessing and changing the boundary date-times of an interval
rep() methods for periods, intervals, and durations

MINOR CHANGES

added a package help page with functions listed by purpose
eseconds(), eminutes(), etc. are aliased to dseconds(), dminutes(), etc. to make it easier to remember they are duration objects.
changed leap.years() to leap_years() to maintain consistent naming scheme

BUG FIXES

rewrote as.period() to create only positive periods.
fixed rollover bug in update.POSIXct()
edited make_diff() to display in days when appropriate, not weeks