Clash Royale CLAN TAG#URR8PPP

Get date for first day of week from year-week number at beginning of year

I know I can convert a year-week number to a date with the following

week = "2018-23"
as.Date(paste(week, "1", sep = "-"), '%Y-%W-%u')
[1] "2018-06-04"


However, if I am looking near the beginning of the year such January 1st of 2014 I will get an NA.

NA

week = "2014-00"
as.Date(paste(week, "1", sep = "-"), '%Y-%W-%u')
[1] NA


I realize this is because there is no 'day 1' for that week as January 1st, 2014 landed on a Wednesday so I would need to change the day number for it to work but it still doesn't return the date I want.

as.Date(paste(week, "3", sep = "-"), '%Y-%W-%u')
[1] '2014-01-01'


I want to get the first date for the full week, namely for it to return `2013-12-30'. Is there any way I can accomplish this as I have many years of data that this instance comes up that I would like to avoid manually editing.

I imagine something with lubridate::floor_date but I don't always know what the day number should be.

lubridate::floor_date

1 Answer
1

I am unable to replicate your NA.

NA

When I run your example with week set to 0 or 1, I get this:

as.Date("2014-00-1", "%Y-%W-%u")
[1] "2014-01-06"
as.Date("2014-01-1", "%Y-%W-%u")
[1] "2014-01-06"


Which makes me think the solution for week-0s is to subtract 7:

as.Date("2014-00-1", "%Y-%W-%u") - 7
[1] "2013-12-30"


Upon reading the documentation for as.Date, this behavior may differ for you and me because of "locale-specific conversions". In any case, you can write your own function to handle your week-0s:

as.Date

myfun <- function(year, week)
if (week == 0)
as.Date(paste(year, "01", "1", sep="-"), "%Y-%W-%u") - 7
else
as.Date(paste(year, week, "1", sep="-"), "%Y-%W-%u")




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