as.Date在以周为基础的日期序列中产生意外结果 [英] as.Date produces unexpected result in a sequence of week-based dates

问题描述

我正在将基于星期的日期转换为基于月的日期.

I am working on the transformation of week based dates to month based dates.

在检查我的工作时，我在数据中发现以下问题，这是由于简单调用as.Date()

When checking my work, I found the following problem in my data which is the result of a simple call to as.Date()

as.Date("2016-50-4", format = "%Y-%U-%u")
as.Date("2016-50-5", format = "%Y-%U-%u")
as.Date("2016-50-6", format = "%Y-%U-%u")
as.Date("2016-50-7", format = "%Y-%U-%u") # this is the problem

前面的代码在前三行中产生正确的日期:

The previous code yields correct date for the first 3 lines:

"2016-12-15"
"2016-12-16"
"2016-12-17"  

最后一行代码可以追溯到1周:

The last line of code however, goes back 1 week:

 "2016-12-11"

任何人都可以解释这里发生了什么吗?

Can anybody explain what is happening here?

推荐答案

使用一年中的一周可能会变得非常棘手.您可以尝试使用ISOweek包转换日期:

Working with week of the year can become very tricky. You may try to convert the dates using the ISOweek package:

# create date strings in the format given by the OP
wd <- c("2016-50-4","2016-50-5","2016-50-6","2016-50-7", "2016-51-1", "2016-52-7")
# convert to "normal" dates
ISOweek::ISOweek2date(stringr::str_replace(wd, "-", "-W"))

结果

#[1] "2016-12-15" "2016-12-16" "2016-12-17" "2016-12-18" "2016-12-19" "2017-01-01"

属于类Date.

请注意，基于ISO周的日期格式为yyyy-Www-d，其中大写字母W在周号之前.要将其与标准的基于月的日期格式yyyy-mm-dd区别开来是必需的.

Note that the ISO week-based date format is yyyy-Www-d with a capital W preceeding the week number. This is required to distinguish it from the standard month-based date format yyyy-mm-dd.

因此，为了使用ISOweek2date()转换OP提供的日期字符串，有必要在第一个连字符后插入W，这是通过在每个字符串中用-W替换第一个-来实现的

So, in order to convert the date strings provided by the OP using ISOweek2date() it is necessary to insert a W after the first hyphen which is accomplished by replacing the first - by -W in each string.

还请注意，ISO星期从星期一开始，并且星期几从1到7编号.属于ISO星期的年份可能与日历年不同.从上面的示例日期中可以看到这一点，其中基于星期的日期2016-W52-7转换为2017-01-01.

Also note that ISO weeks start on Monday and the days of the week are numbered 1 to 7. The year which belongs to an ISO week may differ from the calendar year. This can be seen from the sample dates above where the week-based date 2016-W52-7 is converted to 2017-01-01.

早在2011年，%G，%g，%u和%V格式规范在Windows版本的R中不适用于strptime().这很烦人，因为我必须每周准备报告，包括每周比较.我花了几个小时找到解决ISO周，ISO工作日和ISO年的解决方案.最后，我最终创建了ISOweek程序包，并在CRAN上发布.如今，该软件包仍然有其优点，因为上述格式在输入时被忽略(有关详细信息，请参见?strptime).

Back in 2011, the %G, %g, %u, and %V format specifications weren't available to strptime() in the Windows version of R. This was annoying as I had to prepare weekly reports including week-on-week comparisons. I spent hours to find a solution for dealing with ISO weeks, ISO weekdays, and ISO years. Finally, I ended up creating the ISOweek package and publishing it on CRAN. Today, the package still has its merits as the aforementioned formats are ignored on input (see ?strptime for details).

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