ISOweek {ISOweek}

Week of the year according to ISO 8601

Description

This function returns the year and the week of the year of a given date according to ISO 8601. It is an substitute for the %Y-W%V format which is not implemented on Windows.

Usage

  ISOweek(date)

Arguments

date

Vector which can be coerced to class Date

Details

According to ISO 8601, the year of the week can differ from the calendar year (see the examples).

Value

A character vector of year and week in format "%Y-W%V"

Author(s)

Hatto von Hatzfeld [e-mail], adopted to R by Uwe Block [e-mail]

References

http://www.salesianer.de/util/kalwoch.html

See Also

strptime for a description of the date formats and references on ISO 8601. isoWeekYear for an alternative implementation.

Examples

x <- paste(1999:2011, "-12-31", sep = "")
y <- as.Date(x)
data.frame(date = format(y), week = ISOweek(y))
data.frame(date = x, week = ISOweek(x))