date_xx Vectors

dint provides 4 different S3 classes that inherit from date_xx¹.

date_yq for year-quarter dates
date_yw for year-month dates
date_yw for year-isoweek dates. Please note that the year for isoweeks does not necessarily correspond to the calendar year wikipedia
date_y for storing years. This class exists for consistency and provides little advantage over storing years as bare integers. The main use of this class is in package development when you want to write your own generics and methods for years.

Creation

date_xx vectors can be created using explicit constructors…

date_yq(2015, 1)
#> [1] "2015-Q1"
date_ym(c(2015, 2016), c(1, 2))
#> [1] "2015-M01" "2016-M02"
date_yw(c(2008, 2009), 1)
#> [1] "2008-W01" "2009-W01"

..or through coercion of Dates or integers

as_date_yq(Sys.Date())
#> [1] "2020-Q1"
as_date_yq(20141)   # the last digit is interpreted as quarter
#> [1] "2014-Q1"
as_date_ym(201412)  # the last two digits are interpreted as month
#> [1] "2014-M12"
as_date_yw("2018-01-01")  # anything else that can be parsed by as.Date() works
#> [1] "2018-W01"

Coercion

You can coerce Dates to any date_xx subclass with as_date_**()

d <- as.Date("2018-05-12")
as_date_yq(d)
#> [1] "2018-Q2"
as_date_ym(d)
#> [1] "2018-M05"
as_date_yw(d)
#> [1] "2018-W19"
as_date_y(d)
#> [1] "2018"

Conversely, you can convert date_xx back to R Dates

q <- date_yq(2015, 1)
as.Date(q)
#> [1] "2015-01-01"
as.POSIXlt(q)
#> [1] "2015-01-01 UTC"

as.POSIXct() creates datetimes in UTC/GMT, so the result might not always be as expected, depending on your local timezone.

as.POSIXct(q)
#> [1] "2015-01-01 01:00:00 CET"
as.POSIXct(q, tz = "GMT")
#> [1] "2015-01-01 01:00:00 CET"
print(as.POSIXct(q), tz = "GMT")
#> [1] "2015-01-01 GMT"
print(as.POSIXct(q), tz = "CET")
#> [1] "2015-01-01 01:00:00 CET"

Arithmetic and Sequences

All date_xx support addition, subtraction and sequence generation.

q <- date_yq(2014, 4)
q + 1
#> [1] "2015-Q1"
q - 1
#> [1] "2014-Q3"
seq(q - 2, q + 2)
#> [1] "2014-Q2" "2014-Q3" "2014-Q4" "2015-Q1" "2015-Q2"

m <- date_ym(2014, 12)
m + 1
#> [1] "2015-M01"
m - 1
#> [1] "2014-M11"
seq(m - 2, m + 2)
#> [1] "2014-M10" "2014-M11" "2014-M12" "2015-M01" "2015-M02"

w <- date_yw(2017, 33)
w + 1
#> [1] "2017-W34"
w - 1
#> [1] "2017-W32"
seq(w - 2, w + 2)
#> [1] "2017-W31" "2017-W32" "2017-W33" "2017-W34" "2017-W35"

Accessors

date_xx Components

You can access components of date_xx (e.g the quarter of a date_yq) with accessor functions. You can also use these functions to convert between date_xx vectors.

q <- date_yq(2014, 4)
get_year(q)
#> [1] 2014
get_quarter(q)
#> [1] 4
get_month(q) # defaults to first month of quarter
#> [1] 10
get_isoweek(q)
#> [1] 40

m <- date_ym(2014, 12)
get_year(m)
#> [1] 2014
get_quarter(m)
#> [1] 4
get_month(m)
#> [1] 12
get_isoweek(m)
#> [1] 49

w <- date_yw(2014, 33)
get_year(w)
#> [1] 2014
get_quarter(w)
#> [1] 3
get_month(w)
#> [1] 8
get_isoweek(w)
#> [1] 33

lubridate Compatibility Accessors

If you use lubridate, you can just use the slightly less verbose lubridate accessors

suppressPackageStartupMessages(library(lubridate))

year(q)
#> [1] 2014
quarter(q)
#> [1] 4
month(q)
#> [1] 10

You can get the first and last days of calendar periods with dint

q <- date_yq(2015, 1)
first_of_quarter(q)  # the same as as.Date(q), but more explicit
#> [1] "2015-01-01"
last_of_quarter(q) 
#> [1] "2015-03-31"

These functions work with normal dates

d <- as.Date("2018-05-12")
first_of_year(d)
#> [1] "2018-01-01"
last_of_year(d)
#> [1] "2018-12-31"
first_of_quarter(d)
#> [1] "2018-04-01"
last_of_quarter(d)
#> [1] "2018-06-30"
first_of_month(d)
#> [1] "2018-05-01"
last_of_month(d)
#> [1] "2018-05-31"
first_of_isoweek(d)
#> [1] "2018-05-07"
last_of_isoweek(d)
#> [1] "2018-05-13"

# Alternativeley you can use these:
first_of_yq(2012, 2)
#> [1] "2012-04-01"
last_of_ym(2012, 2)
#> [1] "2012-02-29"
last_of_yw(2011, 52)
#> [1] "2012-01-01"

Formatting

format() Methods

Formatting date_xx vectors is easy and uses a subset of the placeholders of base::strptime() (+ %q for quarters).

q <- date_yq(2014, 4)
format(q, "%Y-Q%q")  # iso/default
#> [1] "2014-Q4"
format(q, "%Y.%q")
#> [1] "2014.4"
format(q, "%y.%q")
#> [1] "14.4"

m <- date_ym(2014, 12)
format(m, "%Y-M%m")  # iso/default
#> [1] "2014-M12"

w <- date_yw(2014, 1)
format(w, "%Y-W%V")  # iso/default
#> [1] "2014-W01"

Shorthands

dint also provides all-in-one functions for common tasks

format_yq(Sys.Date())
#> [1] "2020-Q1"
format_yq_short(Sys.Date())
#> [1] "2020.1"
format_yq_shorter(Sys.Date())
#> [1] "20.1"

format_ym(Sys.Date())
#> [1] "2020-M02"
format_yw(Sys.Date())
#> [1] "2020-W06"

ggplot2: Axis Labels

library(ggplot2)

Labelling date_xx Vectors

dint implements scale_date_**() and date_**_breaks() that provide nicely labeled axes for ggplots by default

q <- data.frame(
  time  = seq(date_yq(2016, 1), date_yq(2016, 4)),
  value = rnorm(4)
)

m <- data.frame(
  time  = seq(date_ym(2016, 8), date_ym(2016, 11)),
  value = rnorm(4)
)

w <- data.frame(
  time  = seq(date_yw(2016, 48), date_yw(2017, 1)),
  value = abs(rnorm(6))
)

w2 <- data.frame(
  time  = seq(date_yw(2016, 1), date_yw(2019, 1)),
  value = abs(rnorm(157))
)

ggplot(q, aes(x = time, y = value))  + 
  geom_point()

ggplot(m, aes(x = time, y = value))  + 
  geom_line() +
  scale_x_date_ym(labels = format_ym_shorter)

ggplot(w, aes(x = time, y = value))  + 
  geom_col()  + 
  scale_x_date_yw(labels = format_yw_iso)

ggplot(w2, aes(x = time, y = value)) + 
  geom_smooth() 
#> `geom_smooth()` using method = 'loess' and formula 'y ~ x'

Labelling Date Vectors

If you use R Date vectors, you can still use the formatting functions supplied by dint to generate nice axis labels.

x <- data.frame(
  time  = seq(as.Date("2016-01-01"), as.Date("2016-08-08"), by = "day"),
  value = rnorm(221)
)

p <- ggplot(
  x,
  aes(
    x = time, 
    y = value)
  ) + geom_point()

p + ggtitle("iso") + ggtitle("default")
p + scale_x_date(labels = format_yq_iso) + ggtitle("date_yq_iso")
p + scale_x_date(labels = format_ym_short) + ggtitle("date_ym_short")
p + scale_x_date(labels = format_yw_shorter) + ggtitle("date_yw_shorter")

Dint: Integer Representations of Calendar Periods

Stefan Fleck

2020-02-06