如何通过POSIXct将日期转换为年/周，并将其转换为一周的第一天?

I want to convert

我想转换

myDate=as.character("2017/02")

which is in the format year/week to a date that is the first day of this week. So I tried:

以年/周为单位，直到本周的第一天。所以我试着:

print(as.POSIXct(myDate,format="%Y/%U"))

However, this gives me

然而,这给了我

[1] "2017-05-03 CEST"

which is certainly not the first day of the second week in 2017.

这当然不是2017年第二周的第一天。

Question: How do I need to change as.POSIXct(myDate,format="%Y/%U") in order to make it work as described above?

问:我需要如何更改as. posixct (myDate,format="%Y/%U")才能让它像上面描述的那样工作?

2 个解决方案

#1

A year and a week is not a proper date. A day would need to be associated with the week. For example:

一年零一周不是一个合适的日期。一天需要和一周联系起来。例如:

myDate=as.character("2017/02")    
as.POSIXct(paste(myDate, "0"),format="%Y/%U %w")

#[1] "2017-01-08 EST"

this assumes the first day of the week is Sunday. If you prefer a Monday then see the %u option.

假设一周的第一天是星期天。如果你更喜欢周一，那么请查看%u选项。

#2

Here a possible approach:

这里的一个可能的方法:

myDate=as.character("2017/02")

Creation of the calendar (yyyy/dd/mm) of indicated year (E.g. 2017)

指定年份的日历(yyyyy /dd/mm)的创建(如2017年)

year_date<-seq.Date(as.Date(paste0(substr(myDate,1,4),"/01/01")),as.Date(paste0(substr(myDate,1,4),"/12/31")),by=1)

Using library ISOweek, this code finds the first day of each week

使用ISOweek库，这个代码可以找到每周的第一天

library("ISOweek")
first_day<-cumsum(ISOweekday(year_date)==1)

Extraction of the first day of the indicated week

提取指定周的第一天

year_date[which(first_day==as.numeric(unlist(strsplit(myDate,split="/"))[2]))[1]]
[1] "2017-01-09"

NB: in this example weeks start on monday

在这个例子中，星期从星期一开始

#1