53rd week of the year in R?
date, dayofweek, r
Solution
The package `ISOweek` manages ISO 8601 style week numberings, converting to and from `Date` objects in `R`. See `ISOweek` for more. Continuing the example dates above, we first need to modify the formatting a bit. They must be in form `yyyy-Www-w` rather than `yyyy-ww`, i.e. `2009-W53-1`. The final digit identifies which day of the week to use in identifying the week, in this case it is the Monday. The week number must be two-digit.
library(ISOweek)
dates <- c("2009-50", "2009-51", "2009-52", "2009-53", "2010-01", "2010-02")
other.dates <- c("2007-53", "2008-53", "2009-53", "2010-53")
dates <- sub("(\\d{4}-)(\\d{2})", "\\1W\\2-1", dates)
other.dates <- sub("(\\d{4}-)(\\d{2})", "\\1W\\2-1", other.dates)
## Check:
dates
# [1] "2009-W50-1" "2009-W51-1" "2009-W52-1" "2009-W53-1" "2010-W01-1"
# [6] "2010-W02-1"
(iso.date <- ISOweek2date(dates)) # deal correctly
# [1] "2009-12-07" "2009-12-14" "2009-12-21" "2009-12-28" "2010-01-04"
# [6] "2010-01-11"
(iso.other.date <- ISOweek2date(other.dates)) # also deals with this
# [1] "2007-12-31" "2008-12-29" "2009-12-28" "2011-01-03"
## Check that back-conversion works:
all(date2ISOweek(iso.date) == dates)
# [1] TRUE
## This does not work for the others, since the 53rd week of
## e.g. 2008 is back-converted to the first week of 2009, in
## line with the ISO 6801 standard.
date2ISOweek(iso.other.date) == other.dates
# [1] FALSE FALSE TRUE FALSE
Problem
I have week-date data in the form `yyyy-ww` where `ww`is the week number in two digits. The data span `2007-01` to `2010-30`. The week counting convention is ISO 8601, which as you can see here on Wikipedia's "Week number" article, occasionally reaches 53 weeks in a year. For example 2009 had 53 weeks by this system, see the week numbers in this ISO 8601 calendar. (See other years; as per the Wikipedia article, 53rd weeks are fairly rare.) Basically I want to read the week date in, convert it to a `Date` object and save this to a separate column in a `data.frame`. As a test, I reconverted the `Date` objects to `yyyy-ww` formats by `format([Date-object], format = "%Y-%W"`, and this threw up an error at `2009-53`. That week fails to be interpreted as a date by `R`. This is very odd, as other years which do not have a 53rd week (in ISO 8601 standard) are converted fine, such as `2007-53`, whereas other years that also do not have a 53rd week (in ISO 8601 standard) also fail, such as `2008-53` The following minimal example demonstrates the issue. Minimal example: ``` dates <- c("2009-50", "2009-51", "2009-52", "2009-53", "2010-01", "2010-02") as.Date(x = paste(dates, 1), format = "%Y-%W %w") # [1] "2009-12-14" "2009-12-21" "2009-12-28" NA "2010-01-04" # [6] "2010-01-11" other.dates <- c("2007-53", "2008-53", "2009-53", "2010-53") as.Date(x = paste(other.dates, 1), format = "%Y-%W %w") # [1] "2007-12-31" NA NA NA ``` The question is, how do I get `R` to accept week numbers in ISO 8601 format? Note: This question summarises a problem I have been struggling with for a few hours. I have searched and found various helpful posts such as this, but none solved the problem.