Author: Stefan Fleck
Date: 2024-11-20

# Dint: Integer Representations of Calendar Periods

#### Stefan Fleck

#### 2024-11-20

    library(dint)

dint helps you with working with year-quarter, year-month and year-isoweek dates. It stores them in an easily human readable integer format, e.q `20141` for the first quarter of 2014 and so forth. If you are already using such integers to represent dates, dint can make many common operations easier for you.

dint is implemented in base R and comes with zero external dependencies. Even if you don’t work with such special dates directly, dint can still help you at formatting dates, labelling plot axes, or getting first / last days of calendar periods (quarters, months, isoweeks).

# date_xx Vectors

dint provides 4 different S3 classes that inherit from `date_xx`1.

- `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] "2024-Q4"
    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 UTC"
    as.POSIXct(q, tz = "GMT")
    #> [1] "2015-01-01 GMT"
    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] "2024-Q4"
    format_yq_short(Sys.Date())
    #> [1] "2024.4"
    format_yq_shorter(Sys.Date())
    #> [1] "24.4"

    format_ym(Sys.Date())
    #> [1] "2024-M11"
    format_yw(Sys.Date())
    #> [1] "2024-W47"

# 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")

1. `date_xx` is just a superclass for all dint date classes, you do not need to use it directly↩︎