Working with dates
Preamble
Importing and working with dates is always tricky, no matter the programming language. fortunately a package called lubridate comes to our rescue when working in R. This package is part of the tidyverse packages.
library(tidyverse)As stated in r4ds (the older version):
“There are three types of date/time data that refer to an instant in time:
- A date. Tibbles print this as “date”
- A time within a day. Tibbles print this as “time”.
- A date-time is a date plus a time: it uniquely identifies an instant in time (typically to the nearest second). Tibbles print this as “dttm”. Elsewhere in R these are called POSIXct, but I don’t think that’s a very useful name.”
today() # date
now () # datetime
# generating dates from strings - different format, same date
ymd("2017-08-23")
ymd("20170823")
ymd("20132308") # returns NA, why?
ymd("20170229") # returns NA, why?
dmy("23-8-2017")
mdy("8/23/2017")
mdy("Jun-3-17")
mdy("June-3-17")
mdy("Júní-3-17") # returns NA
make_date(2017, 8, 23)
# date-time
ymd_hm("2017/08/23 08:01")
ymd_hms("2017/08/23 08:01:59")
ymd_hms("20170823 080159")
make_datetime(2017, 8, 23, 8, 1, 59)
# sequence of dates
seq(ymd("2017-08-23"), ymd("2021-01-04"), by = "year")
seq(ymd("2017-08-23"), ymd("2021-01-04"), by = "quarter")
seq(ymd("2017-08-23"), ymd("2021-01-04"), by = "month")
seq(ymd("2017-08-23"), ymd("2021-01-04"), by = "week")
seq(ymd("2017-08-23"), ymd("2021-01-04"), by = "day")
seq(ymd_hm("2017-08-23 12:00"), ymd_hm("2017-08-24 00:00"), by = "hour")
# etc.
# problems
ymd(c("2023-06-27", "2023-27-06"))We deal with a case exmple of messy dates further downstream . ## Datetime components
Once we have our date-time variable correctly setup we can start making something (possibly) useful with it. Consider:
dt <- now()
dt
as_date(dt)
year(dt)
quarter(dt)
month(dt)
month(dt, label = TRUE, abbr = FALSE)
Sys.getlocale("LC_TIME") # get your system setup for date time
week(dt)
wday(dt)
wday(dt, label = TRUE, abbr = TRUE)
day(dt)
hour(dt)
minute(dt)
second(dt)
pm(dt)
am(dt)Your can “floor” dates, like put all days to the first date of the month:
floor_date(dt, unit = "month")