将星期数转换为日期，将星期数添加到今天的日期

Question

Sorry, this has been asked multiple times but none of the posted replies have worked for me. I am trying to convert week number to date or ideally a month name using as.Date function. However I keep getting the same result no matter what week I put in and I just cannot figure out why. Any help is appreciated

```R
as.Date(x = 03, format = "%W",origin = "2019-01-01")
# This results in "2019-09-16"

as.Date(x = 4, format = "%W",origin = "2019-01-01")
# This results in "2019-09-17"

as.Date(x = 12, format = "%w",origin = "2019-01-01")
# This results in "2019-09-25"

as.Date(x = 12, format = "%W",origin = "2018-01-01")
# This results in "2019-09-25"
```

Even when I change the year, it produces the same output. It seems to be adding today's date (13th) to the week number. The most frustrating part is that this is an old code, which has been working perfectly as of yesterday

Answer 1

From the help: "If the date string does not specify the date completely, the returned answer may be system-specific. The most common behavior is to assume that a missing year, month or day is the current one."

The easiest way to get around this is to specify the day and then convert:

 as.Date(x = paste(3, "0"), format = "%W %w")
[1] "2019-01-15"

 as.Date(x = paste(10, "0"), format = "%W %w")
[1] "2019-03-04"

You will also need to specify the year, if you change it from the current year.

as.Date(x = paste(10, "0 2018"), format = "%W %w %Y")
[1] "2018-03-04"

You can substitute in your vector in for the 3 or 10 in the above examples.