datey: Create a 'datey'

In datey: Exact Date and Duration Arithmetic on an Annual Grid

Create a datey

Description

To create a datey use one of the following:

• start_day() and end_day() are the points in time at the start and end of the day respectively.

• mid_day() is the the middle of the day, commonly used to represent a point in time during the day.

• datey() is the underlying S3 generic function. start_day(), mid_day() and end_day() call through to datey with an explicit day_fraction or 0, 0.5 and 1 respectively.

The generic types are as follows:

• double and integer. These are interpreted as calendar year, optionally with a fractional part in the case of double.

  Valid years are from 1000 to 3000 (although the only legal date in 3000 is the start of 3000-01-01).

  Either

  (a) month and day (and for datey(), day_fraction) parameters are all provided, in which case x must be integral, or

  (b) none of those parameters are provided, in which case x is interpreted as a fractional calendar year and rounded to the nearest 1 / 534 360 of a year (Banker's rounding). This unit is called a click and is the resolution of all datey arithmetic. For instance, datey(2000.5) means halfway through the year 2000.

• Date. This base R date type is interpreted strictly. (It is possible to end up with an unintentionally fractional underlying value, e.g. by taking a mean of Dates.) A day_fraction argument is always required.

• POSIXct and POSIXlt. How these base R date-time types are interpreted depends on whether a day_fraction is provided.

  If day_fraction is provided then these are interpreted strictly using the date component only – the time component is ignored completely.

  If day_fraction is not provided then the day fraction is determined using the hours, minutes, and seconds. For instance, datey(as.POSIXct("2000-03-21 12:00")) means the middle of 2000-03-21.

• character. How text is parsed depends on whether a day_fraction is provided.

  If day_fraction is provided then the text must be in ISO 8601 extended format, i.e. YYYY-MM-DD.

  If day_fraction is not provided then the text must be formatted as ⁠YYYY-MM-DD[.F..].⁠, where ⁠[.F...]⁠ is the optional day fraction. This means that e.g. "2000-01-01" represents the start of 1 January 2000.

  If blank_is_NA is TRUE then blanks are treated as NA (regardless of strict).

• datey. This is interpreted as is but with the optional day_fraction override. Note that a day_fraction of 1 will add a day to a day boundary, even if it was originally defined as an end day.

The lengths of vector arguments must be multiples of each other.

Beware that end_day() will add a day to a datey that is already on a day boundary, even if it was originally defined as an end day.

There is no is_end_day() predicate: end days are stored identically to the start of the following day, so is_start_day() is the correct test.

NA arguments of the appropriate type result in NA_datey_ – they do not stop execution (regardless of strict). Note that NA is logical and therefore it will cause an error.

Usage

datey(x, ...)

## Default S3 method:
datey(x, ...)

## S3 method for class 'datey'
datey(x, day_fraction = NULL, strict = TRUE, ...)

## S3 method for class 'integer'
datey(x, month = NULL, day = NULL, day_fraction = NULL, strict = TRUE, ...)

## S3 method for class 'double'
datey(x, month = NULL, day = NULL, day_fraction = NULL, strict = TRUE, ...)

## S3 method for class 'Date'
datey(x, day_fraction, strict = TRUE, ...)

## S3 method for class 'POSIXct'
datey(x, day_fraction = NULL, strict = TRUE, ...)

## S3 method for class 'POSIXlt'
datey(x, day_fraction = NULL, strict = TRUE, ...)

## S3 method for class 'character'
datey(x, day_fraction = NULL, strict = TRUE, blank_is_NA = FALSE, ...)

start_day(x, month = NULL, day = NULL, strict = TRUE, blank_is_NA = FALSE)

mid_day(x, month = NULL, day = NULL, strict = TRUE, blank_is_NA = FALSE)

end_day(x, month = NULL, day = NULL, strict = TRUE, blank_is_NA = FALSE)

Arguments

x	The argument to convert to a datey.
...	Not used.
day_fraction	The day_fraction override. Defaults to NULL except for the Date type, in which case it must always be provided. If day_fraction is provided (which is implicitly the case for start_day(), mid_day() and end_day()) then x is used solely to derive the calendar year, month and day, while day_fraction provides the position in the day. day_fraction must lie in the inclusive interval [0,1], with 0 meaning the start of the day, 0.5 meaning the middle of the day, and 1 meaning the end of the day (which is identical to the start of the next day). For text this means that there should be no trailing fraction, e.g. start_day("2020-01-01"). If day_fraction is not provided then x is used to derive both the calendar year, month, day and the day fraction.
strict	How non-compliant non-NA inputs should be handled. If strict is TRUE – the default – then execution is stopped. If strict is FALSE then NA is returned.
month, day	The month (1–12) and day (1–31). Valid only for for numeric x. If one of month or day is provided then both must be and, for datey(), day_fraction must also be provided.
blank_is_NA	Whether "" should be treated as NA (regardless of strict). When x is "" then if blank_is_NA is TRUE then "" results in NA, otherwise execution is stopped. Defaults to FALSE. Valid only for for character x.

Value

A vector of datey.

See Also

durationy, datey_interval, text_from_datey, as_years_datey, datey_components, is_xxx_day, is_leap_year, is_NA, ops, vignette("why-datey", package = "datey") for the annual-grid design, vignette("datey", package = "datey") for a worked introduction

Examples

start_day(2001, 2, 3)
mid_day(2001, 2, 3)
end_day(2001, 2, 3)

# Must specify month and day for a numeric if day_fraction is provided
# implicitly or explicitly:
try(start_day(2001))
try(mid_day(2001))
try(end_day(2001))
try(datey(2001, day_fraction = 0))

datey(2000) # Start of a year
datey(2000.5) # Middle of a leap year
datey(2001.5) # Middle of a non-leap year

# Convert base R date
r_date <- as.Date("2001-02-03")
c(start_day(r_date), mid_day(r_date), end_day(r_date))
try(datey(r_date)) # Must specify day_fraction for a `Date`

# Convert base R datetime
c_date <- as.POSIXct("2001-02-03 12:00:00") # Midday!
c(start_day(c_date), mid_day(c_date), end_day(c_date))
# An R datetime implies a position within a day:
datey(c_date) # 2001-02-03.5

# Use `strict` to control error behaviour for invalid years:
try(end_day(0999, 12, 31))
try(datey(3000.1))
end_day(0999, 12, 31, strict = FALSE)
datey(3000.1, strict = FALSE)

# NAs are passed through regardless of `strict`
# (provided they are numeric)
end_day(NA_real_, 12, 31, strict = TRUE)
datey(NA_real_, strict = FALSE)

# Text:
start_day("2001-02-03")
mid_day("2001-02-03")
end_day("2001-02-03")
datey("2001-02-03")
datey("2001-02-03.0")
datey("2001-02-03", day_fraction = 0)
datey("2001-02-03.5")
datey("2001-02-03", day_fraction = 0.5)

# Text round trips:
t <- datey(2001.234)
identical(t, datey(as.character(t))) # TRUE

# Day fraction cannot be present
# both in the text and as an argument
# implicitly or explicitly:
try(start_day("2001-02-03.0"))
try(datey("2001-02-03.0", day_fraction = 0))

# Handling blanks:
try(start_day(""))
start_day("", blank_is_NA = TRUE)

# Invalids:
try(mid_day("abc"))
try(mid_day("0999-01-01"))
end_day("abc", strict = FALSE) # NA
end_day("0999-01-01", strict = FALSE) # NA

datey documentation built on July 14, 2026, 5:06 p.m.