# practice with lubridate
# convert formatted strings to dates
library(lubridate)

date_ymd <- ymd_hms("2017-12-28 10:26:20")

date_mdy <- mdy_hm("12/28/17 11:44")

date_hm1 <- dmy_hm("28.12.17 9:30AM")

date_hm2 <- dmy_hm("28.12.17 9:30PM")

# there are functional available for just specifying a date also, numbers can be used as input to these functions


mdy("March 6, 2015")

dmy("06/03/2015")

dmy(06032015)

ydm("1988/21/2")


# produces objects of class DATE
d_made <- make_date(year = 2018, month = 9, day = 24)

# produces objects of class DATETIME
dt <- make_datetime(year = 2018, month = 9, day = 24,
                    hour = 13L, min = 15L)

# Extract pieces from the date
year(dt) #extract year
month(dt) # extract month
mday(dt) # extract month
yday(dt) #extract day count for the year
wday(dt)  #returns the day of the week as a decimal
wday(dt, label=TRUE)  #set label to TRUE to get string abbr.

hour(dt) # extract the hour from the dt
minute(dt) #extract the minute from dt
second(dt) #extract the second from dt

dt1 <- dt
# these functions can also be use for setting values
year(dt1) <- 2017

month(dt1) <- 7

day(dt1) <- 4

# convert to a date class with the date function
dd <- date(dt1)

# check for a leap year
leap_year(c(dt1,dt))

# get current datetime using different packages
lubridate::today()
# get pieces of today's date
week <- wday(today(),label=TRUE,abbr = FALSE)

base::date()

Sys.Date()

Sys.timezone()

now()

# determin if a datetime is in am
am(now()) # full datetime - should return TRUE if run before noon, FALSE if run after 12:00pm

am(today()) # today is only a date - time defaults to beginning of the day

# create a difftime object for a specific number of units
make_difftime(day=31)

# create an interval object, need a start , end date
x <- interval(ymd("2017-01-01"), ymd("2009-08-01"))
int_start(x)
int_end(x)
int_shift(x, duration(days=14))
#interval
int_length(x)
as.duration(x)
x2 <- interval(ymd("2011-01-01"), ymd("2010-08-01"))
int_overlaps(x,x2) # overlap in 2 intervals
dds <- now() + days(1:10)
int_diff(dds)

as.duration(10) # numeric
dur <- duration(hours = 10, minutes = 6)
as.numeric(dur, "hours")
as.numeric(dur, "minutes")
# calculate the time interval between 2 datetime

# time zones
OlsonNames()

meeting <- ymd_hms("2018-09-21 15:00:00", tz = "Europe/Paris")
with_tz(meeting, "US/Eastern")

# lubridate introduces two other time objects periods and durations. Durations allow you to precisely calculate the difference between date time objects, using specific definitions like there are 365 days in a year. Period allows the length of a year to fluctuate between 365 and 366.

leap_year(2011) ## regular year no leap year

ymd(20110101) + dyears(1) # add a duration year

ymd(20110101) + years(1) # add a period year


leap_year(2012) ## leap year

ymd(20120101) + dyears(1) # last day of 2012

ymd(20120101) + years(1) # first day of 2013