`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()`

is the US CDC version of epidemiological week. It
follows same rules as `isoweek()`

but starts on Sunday. In other parts of
the world the convention is to start epidemiological weeks on Monday,
which is the same as `isoweek`

.

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

#> [1] 13

week(x) <- 1
week(x) <- 54
week(x) > 3

#> [1] FALSE