这与我的问题POSIX date from dates in weekly time format直接相关。
但是，在这个问题中，我想具体询问如何将ISO 8601周数映射到一年中的月份数。
对我来说，似乎不可能和/或涉及一些非直观的黑客攻击（甚至这些都不能真正可靠地工作），因此 IMO应被视为需要修复的东西在基地R 。如果我错了，请纠正我，不过
编辑：似乎问题与在Windows上运行和/或您所在的语言环境（标准德语，在我的情况下）密切相关
posix <- as.POSIXct(c("2015-12-24", "2015-12-31", "2016-01-01", "2016-01-08"))
(yw <- format(posix, "%Y-%V"))
# [1] "2015-52" "2015-53" "2016-53" "2016-01"
ywd <- sprintf("%s-1", yw)
(as.POSIXct(ywd, format = "%Y-%V-%u"))
# [1] "2015-01-12 CET" "2015-01-12 CET" "2016-01-12 CET" "2016-01-12 CET"
# -> utterly wrong!!!
ywd <- sprintf("%s-4", yw)
(as.POSIXct(ywd, format = "%Y-%V-%u"))
# -> still wrong -> the day of the week is not the reason
# -> no way to use ISO 8601 convention to map week of the year to month of the year
为了尽职尽责：在尝试使用美国或英国惯例时也不可能：
(yw <- format(posix, "%Y-%U"))
# [1] "2015-51" "2015-52" "2016-00" "2016-01"
ywd <- sprintf("%s-1", yw)
(as.POSIXct(ywd, format = "%Y-%U-%u"))
# [1] "2015-12-21 CET" "2015-12-28 CET" NA "2016-01-04 CET"
# -> NA problem for week 00
ywd <- sprintf("%s-4", yw)
# -> does not work for week 00
(as.POSIXct(ywd, format = "%Y-%U-%u"))
# The day of the week is not the reason
# -> no way to use this convention to reliably map week of the year to month of the year
(yw <- format(posix, "%Y-%W"))
# [1] "2015-51" "2015-52" "2016-00" "2016-01"
ywd <- sprintf("%s-1", yw)
(as.POSIXct(ywd, format = "%Y-%W-%u"))
# [1] "2015-12-21 CET" "2015-12-28 CET" NA "2016-01-04 CET"
# -> NA problem for week 00
ywd <- sprintf("%s-4", yw)
# -> does not work for week 00
(as.POSIXct(ywd, format = "%Y-%W-%u"))
# The day of the week is not the reason
# -> no way to use this convention to reliably map week of the year to month of the year
> sessionInfo()
R version 3.3.2 (2016-10-31)
Platform: x86_64-w64-mingw32/x64 (64-bit)
Running under: Windows >= 8 x64 (build 9200)
locale:
[1] LC_COLLATE=German_Germany.1252 LC_CTYPE=German_Germany.1252 LC_MONETARY=German_Germany.1252
[4] LC_NUMERIC=C LC_TIME=English_United States.1252
attached base packages:
[1] stats graphics grDevices utils datasets methods base
other attached packages:
[1] fva_0.1.0 digest_0.6.10 readxl_0.1.1 dplyr_0.5.0 plyr_1.8.4 magrittr_1.5
[7] memoise_1.0.0 testthat_1.0.2 roxygen2_5.0.1 devtools_1.12.0
loaded via a namespace (and not attached):
[1] Rcpp_0.12.8 lubridate_1.6.0 assertthat_0.1 packrat_0.4.8-1 crayon_1.3.2 withr_1.0.2
[7] R6_2.2.0 DBI_0.5-1 stringi_1.1.2 rstudioapi_0.6 tools_3.3.2 stringr_1.1.0
[13] tibble_1.2
> devtools::session_info()
Session info -----------------------------------------------------------------------------------------------
setting value
version R version 3.3.2 (2016-10-31)
system x86_64, mingw32
ui RStudio (1.0.136)
language en
collate German_Germany.1252
tz Europe/Berlin
date 2017-01-12
Packages ---------------------------------------------------------------------------------------------------
package * version date source
assertthat 0.1 2013-12-06 CRAN (R 3.3.2)
crayon 1.3.2 2016-06-28 CRAN (R 3.3.2)
DBI 0.5-1 2016-09-10 CRAN (R 3.3.2)
devtools * 1.12.0 2016-06-24 CRAN (R 3.3.2)
digest * 0.6.10 2016-08-02 CRAN (R 3.3.2)
dplyr * 0.5.0 2016-06-24 CRAN (R 3.3.2)
fva * 0.1.0 <NA> local
lubridate 1.6.0 2016-09-13 CRAN (R 3.3.2)
magrittr * 1.5 2014-11-22 CRAN (R 3.3.2)
memoise * 1.0.0 2016-01-29 CRAN (R 3.3.2)
packrat 0.4.8-1 2016-09-07 CRAN (R 3.3.2)
plyr * 1.8.4 2016-06-08 CRAN (R 3.3.2)
R6 2.2.0 2016-10-05 CRAN (R 3.3.2)
Rcpp 0.12.8 2016-11-17 CRAN (R 3.3.2)
readxl * 0.1.1 2016-03-28 CRAN (R 3.3.2)
roxygen2 * 5.0.1 2015-11-11 CRAN (R 3.3.2)
stringi 1.1.2 2016-10-01 CRAN (R 3.3.2)
stringr 1.1.0 2016-08-19 CRAN (R 3.3.2)
testthat * 1.0.2 2016-04-23 CRAN (R 3.3.2)
tibble 1.2 2016-08-26 CRAN (R 3.3.2)
withr 1.0.2 2016-06-20 CRAN (R 3.3.2)
答案 0 :(得分：1)
披露：如this answer中所述，我创建了ISOweek package来处理基于ISO 8601周的日期。
这个问题包含几个缺陷：
OP使用
创建了样本数据posix <- as.POSIXct(c("2015-12-24", "2015-12-31", "2016-01-01", "2016-01-08"))
(yw <- format(posix, "%Y-%V"))
[1] "2015-52" "2015-53" "2016-53" "2016-01"
格式规范%Y返回日历年，显然第三个元素是错误的。
使用正确的格式规范%G，我们得到
(yw <- format(posix, "%G-%V"))
[1] "2015-52" "2015-53" "2015-53" "2016-01"
仅提供基于ISO周的年份和周数 ，不用 一周将产生含糊不清的结果
这可以用（校正的）样本数据证明，该数据现在包含OP自己的（非标准）年 - 周格式的连续三周：
yw
[1] "2015-52" "2015-53" "2016-01"
借助ISOweek2date()包中的ISOweek功能，数据会转换为日历日期。请注意，ISOweek2date()要求以yyyy-Www-d格式（包括星期几）生成完整的ISO 8601基于工作日的日期。如果我们选择一周的第一天（星期一），我们会得到：
library(ISOweek)
library(magrittr)
yw %>%
# insert "W" to conform with ISO 8601 format
sub("-", "-W", .) %>%
# append day of week
paste0("-1") %>%
# convert to class Date and print as yyyy-mm
ISOweek2date() %>%
format("%Y-%m")
[1] "2015-12" "2015-12" "2016-01"
现在，我们使用一周中的最后一天（星期日）重复此操作：
yw %>%
sub("-", "-W", .) %>%
paste0("-7") %>%
ISOweek2date() %>%
format("%Y-%m")
[1] "2015-12" "2016-01" "2016-01"
请注意，第二个元素现在指的是2016年1月而不是2015年12月，因为53周的星期日是1月，而本周的星期一仍然是12月。
答案 1 :(得分：0)
非常确定基础R 以外的其他内容需要更改（请参阅结尾处的注释）：
some_dates <- as.POSIXct(c("2015-12-24", "2015-12-31", "2016-01-01", "2016-01-08"))
(year_week <- format(some_dates, "%Y %U"))
## [1] "2015 51" "2015 52" "2016 00" "2016 01"
(year_week_day <- sprintf("%s 1", year_week))
## [1] "2015 51 1" "2015 52 1" "2016 00 1" "2016 01 1"
(as.POSIXct(year_week_day, format = "%Y %U %u"))
## [1] "2015-12-21 EST" "2015-12-28 EST" "2016-01-04 EST" "2016-01-04 EST"
它也适用于破折号：
(year_week <- format(some_dates, "%Y-%U"))
## [1] "2015-51" "2015-52" "2016-00" "2016-01"
(year_week_day <- sprintf("%s-1", year_week))
## [1] "2015-51-1" "2015-52-1" "2016-00-1" "2016-01-1"
(as.POSIXct(year_week_day, format = "%Y-%U-%u"))
## [1] "2015-12-21 EST" "2015-12-28 EST" "2016-01-04 EST" "2016-01-04 EST"
并且，尽管短划线是OK ISO形式，但当各种值不是> 12或<0
时，它们会导致读者混淆注意
由于评论主题表明这是Windows上的行为：
(year_week <- format(some_dates, "%Y-%U"))
## [1] "2015-51" "2015-52" "2016-00" "2016-01"
(year_week_day <- sprintf("%s-1", year_week))
## [1] "2015-51-1" "2015-52-1" "2016-00-1" "2016-01-1"
(as.POSIXct(year_week_day, format = "%Y-%U-%u"))
## [1] "2015-12-21 PST" "2015-12-28 PST" NA "2016-01-04 PST"
（Windows 10 64bit，R 3.3.2 for me / this example）
答案 2 :(得分：0)
R日期时间格式参数?strptime的文档说输入时将忽略“％V”。