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```
#' The aweek class
#'
#' The aweek class is a character or factor in the format YYYY-Www(-d) with a
#' "week_start" attribute containing an integer specifying which day of the ISO
#' 8601 week each week should begin.
#'
#' @param x an object of class `aweek`
#' @param ... a series of `aweek` objects, characters, or Dates, (unused in `print.aweek()`)
#' @param recursive,use.names parameters passed on to [unlist()]
#'
#' @return an object of class `aweek`
#'
#' @details Weeks differ in their start dates depending on context. The ISO
#' 8601 standard specifies that Monday starts the week
#' (<https://en.wikipedia.org/wiki/ISO_week_date>) while the US CDC uses
#' Sunday as the start of the week
#' (<https://stacks.cdc.gov/view/cdc/22305>). For
#' example, MSF has varying start dates depending on country in order to
#' better coordinate response.
#'
#' While there are packages that provide conversion for ISOweeks and epiweeks,
#' these do not provide seamless conversion from dates to epiweeks with
#' non-standard start dates. This package provides a lightweight utility to
#' be able to convert each day.
#'
#' \subsection{Calculation of week numbers}{
#'
#' Week numbers are calculated in three steps:
#'
#' 1. Find the day of the week, relative to the week_start (d). The day of the
#' week (d) relative to the week start (s) is calculated using the ISO week
#' day (i) via `d = 1L + ((i + (7L - s)) %% 7L)`.
#' 2. Find the date that represents midweek (m). The date that represents
#' midweek is found by subtracting the day of the week (d) from 4 and
#' adding that number of days to the current date: `m = date + (4 - d)`.
#' 3. Find the week number (w) by counting the number of days since 1 January
#' to (m), and use integer division by 7: `w = 1L + ((m - yyyy-01-01) %/% 7)`
#'
#' For the weeks around 1 January, the year is determined by the week number.
#' If the month is January, but the week number is 52 or 53, then the year for
#' the week (YYYY) is the calendar year (yyyy) minus 1. However, if the month
#' is December, but the week number is 1, then the year for the week (YYYY) is
#' the calendar year (yyyy) plus 1.
#'
#' }
#' \subsection{Structure of the aweek object}{
#'
#' The aweek object is a character vector in either the precise ISO week
#' format (YYYY-Www-d) or imprecise ISO week format (YYYY-Www) with
#' a `week_start` attribute indicating which ISO week day the week begins.
#' The precise ISO week format can be broken down like this:
#'
#' - **YYYY** is an ISO week-numbering year, which is the year relative to
#' the week, not the day. For example, the date 2016-01-01 would be
#' represented as 2015-W53-5 (ISO week), because while the date is in the
#' year 2016, the week is still part of the final week of 2015.
#' - W**ww** is the week number, prefixed by the character "W". This ranges
#' from 01 to 52 or 53, depending on whether or not the year has 52 or 53
#' weeks.
#' - **d** is a digit representing the weekday where 1 represents the first
#' day of the week and 7 represents the last day of the week. #'
#' The attribute `week_start` represents the first day of the week as an ISO
#' week day. This defaults to 1, which is Monday. If, for example, an aweek
#' object represented weeks starting on Friday, then the `week_start`
#' attribute would be 5, which is Friday of the ISO week.
#'
#' Imprecise formats (YYYY-Www) are equivalent to the first day of the week.
#' For example, 2015-W53 and 2015-W53-1 will be identical when converted to
#' date.
#'
#' }
#'
#' @note when combining aweek objects together, you must ensure that they have
#' the same week_start attribute. You can use [change_week_start()] to adjust
#' it.
#'
#'
#' @export
#' @aliases aweek-class
#' @rdname aweek-class
#' @seealso [date2week()], [get_aweek()], [as.Date.aweek()], [change_week_start()]
#' @examples
#' d <- as.Date("2018-12-20") + 1:40
#' w <- date2week(d, week_start = "Sunday")
#' print(w)
#'
#' # subsetting acts as normal
#' w[1:10]
#'
#' # Combining multiple aweek objects will only work if they have the same
#' # week_start day
#' c(w[1], w[3], w[5], as.aweek(as.Date("2018-12-01"), week_start = "Sunday"))
#'
#' # differing week_start days will throw an error
#' mon <- date2week(as.Date("2018-12-01"), week_start = "Monday")
#' mon
#' try(c(w, mon))
#'
#' # combining Dates will be coerced to aweek objects under the same rules
#' c(w, Sys.Date())
#'
#' # truncated aweek objects will be un-truncated
#' w2 <- date2week(d[1:5], week_start = "Sunday", floor_day = TRUE)
#' w2
#' c(w[1:5], w2)
print.aweek <- function(x, ...) {
tmp <- week2date("2019-W08-1", attr(x, "week_start"))
cat(sprintf("<aweek start: %s>\n", format(tmp, "%A")))
y <- x
attr(x, "week_start") <- NULL
class(x) <- class(x)[class(x) != "aweek"]
NextMethod("print")
invisible(y)
}
#' @export
#' @param i index for subsetting an aweek object.
#' @rdname aweek-class
`[.aweek` <- function(x, i) {
cl <- oldClass(x)
ws <- attr(x, "week_start")
xx <- NextMethod("[")
attr(xx, "week_start") <- ws
oldClass(xx) <- cl
xx
}
#' @export
#' @rdname aweek-class
`[[.aweek` <- function(x, i) {
cl <- oldClass(x)
ws <- attr(x, "week_start")
xx <- NextMethod("[[")
attr(xx, "week_start") <- ws
oldClass(xx) <- cl
xx
}
#' @export
#' @param value a value to add or replace in an aweek object
#' @rdname aweek-class
`[<-.aweek` <- function(x, i, value) {
ws <- attr(x, "week_start")
cl <- oldClass(x)
if (inherits(value, "aweek")) {
if (ws != attr(value, "week_start")) {
stop("aweek objects must have the same week_start attribute")
}
}
if (inherits(value, "character")) {
value <- as.aweek(value, week_start = ws)
}
if (inherits(value, "factor")) {
value <- as.character(value)
stop_if_not_aweek_string(value)
value <- get_aweek(week = int_week(value),
year = int_year(value),
day = int_wday(value),
week_start = ws)
}
if (inherits(value, c("Date", "POSIXt"))) {
value <- date2week(value, week_start = ws)
}
if (!is.null(value) && all(is.na(value))) {
value <- as.aweek(as.character(value), week_start = ws)
}
if (!inherits(value, "aweek")) {
stop(sprintf("Cannot add an object of class '%s' to an aweek object",
paste(class(value), collapse = ", ")))
}
xx <- NextMethod("[")
attr(xx, "week_start") <- ws
oldClass(xx) <- cl
xx
}
#' @export
#' @rdname aweek-class
as.list.aweek <- function(x, ...) {
xx <- NextMethod("as.list")
xx <- lapply(xx, function(i, ws, cl){
attr(i, "week_start") <- ws
oldClass(i) <- cl
i
}, ws = attr(x, "week_start"), cl = oldClass(x))
xx
}
#' @export
#' @rdname aweek-class
trunc.aweek <- function(x, ...) {
if (inherits(x, "factor")) {
levels(x) <- gsub("\\-\\d", "", levels(x))
} else {
x <- gsub("\\-\\d", "", x)
}
x
}
#' @export
#' @rdname aweek-class
rep.aweek <- function(x, ...) {
ws <- attr(x, "week_start")
cl <- oldClass(x)
xx <- NextMethod("rep")
attr(xx, "week_start") <- ws
oldClass(xx) <- cl
xx
}
#' @export
#' @rdname aweek-class
c.aweek <- function(..., recursive = FALSE, use.names = TRUE) {
# Find all the aweek objects and test that they all have the same week_start
# attribute. Throw an error if this isn't true
the_dots <- list(...)
week_start <- get_week_start(the_dots[[1]])
aweeks <- vlogic(the_dots, inherits, "aweek")
identical_week_starts <- vapply(the_dots[aweeks], get_week_start, integer(1)) == week_start
if (!all(identical_week_starts)) {
stop("All aweek objects must have the same week_start attribute. Please use change_week_start() to adjust the week_start attribute if you wish to combine these objects.")
}
# Find all the dates and convert them to aweek objects
dates <- vlogic(the_dots, inherits, c("Date", "POSIXt"))
the_dots[dates] <- lapply(the_dots[dates], date2week, week_start = week_start)
# convert everything to characters and unlist them
res <- unlist(lapply(the_dots, as.character), recursive = recursive, use.names = FALSE)
date_chars <- grepl("[0-9]{4}-[0-9]{2}-[0-9]{2}", res, perl = TRUE)
res[date_chars] <- as.character(date2week(res[date_chars], week_start = week_start))
# convert the characters to aweek objects
out <- get_aweek(week = int_week(res),
year = int_year(res),
day = int_wday(res),
start = week_start,
week_start = week_start
)
names(out) <- names(res)
out
}
```

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