#lubridate

lubridate makes it easier to work with dates and times by providing
functions to identify and parse date-time data, extract and modify
components of a date-time (years, months, days, hours, minutes,
and seconds), perform accurate math on date-times, handle time zones and
Daylight Savings Time. lubridate has a consistent, memorable syntax that
makes working with dates less frustrating.

lubridate 1.1.0 introduces extensive changes, which are summarized below

Version 1.1.0
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* 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 periods, durations, and intervals. 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/hadley/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 acheive 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.

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