week() returns the number of complete seven day periods that have occurred between the date and January 1st, plus one. isoweek() returns the week as it would appear in the ISO 8601 system, which uses a reoccurring leap week. epiweek() returns the week as it conventional in epidemiology. Epiweek follows same rules as isoweek() but starts on Sunday.

week(x)

week(x) <- value

isoweek(x)

epiweek(x)

Arguments

x

a date-time object. Must be a POSIXct, POSIXlt, Date, chron, yearmon, yearqtr, zoo, zooreg, timeDate, xts, its, ti, jul, timeSeries, or fts object.

value

a numeric object

Value

the weeks element of x as an integer number

References

http://en.wikipedia.org/wiki/ISO_week_date http://www.cmmcp.org/epiweek.htm

See also

isoyear()

Examples

x <- ymd("2012-03-26") week(x)
#> [1] 13
week(x) <- 1 week(x) <- 54 week(x) > 3
#> [1] FALSE