strptime，as.POSixct和as.Date返回意外的不適用

Question

當我嘗試使用以下格式解析時間戳時：「Thu Nov 8 15:41:45 2012」，只返回NA。

我使用的是Mac OS X R 2.15.2和Rstudio 0.97.237。我的操作系統的語言是荷蘭語：我認爲這與它有關。

當我嘗試strptime，NA返回：

var <- "Thu Nov 8 15:41:45 2012" 
strptime(var, "%a %b %d %H:%M:%S %Y") 
# [1] NA 

也不對as.POSIXct工作：

as.Date("Thu Nov 8 2012", "%a %b %d %Y") 
# [1] NA 

：

as.POSIXct(var, "%a %b %d %H:%M:%S %Y") 
# [1] NA 

我還對以上但沒有%H:%M:%S組件串試圖as.Date

任何想法我可能做錯了什麼？

Answer 1

我認爲這完全是你猜對的，strptime由於你的語言環境不能解析你的日期時間字符串。您的字符串包含縮寫星期幾（%a）和縮寫月份名稱（%b）。這些時間規範?strptime描述：

Details

%a : Abbreviated weekday name in the current locale on this platform

%b : Abbreviated month name in the current locale on this platform.

"Note that abbreviated names are platform-specific (although the standards specify that in the C locale they must be the first three letters of the capitalized English name:"

"Knowing what the abbreviations are is essential if you wish to use %a , %b or %h as part of an input format: see the examples for how to check."

See also

[...] locales to query or set a locale.

的locales問題也是相關as.POSIXct，as.POSIXlt和as.Date。

從?as.POSIXct：

Details

If format is specified, remember that some of the format specifications are locale-specific, and you may need to set the LC_TIME category appropriately via Sys.setlocale . This most often affects the use of %b , %B (month names) and %p (AM/PM).

從?as.Date：

Details

Locale-specific conversions to and from character strings are used where appropriate and available. This affects the names of the days and months.

---

因此，如果平日月份名字符串中那些在當前區域設置，strptime，as.POSIXct和as.Date不同無法正確解析字符串並返回NA。

但是，您可以通過改變locales解決這個問題：

# First save your current locale 
loc <- Sys.getlocale("LC_TIME") 

# Set correct locale for the strings to be parsed 
# (in this particular case: English) 
# so that weekdays (e.g "Thu") and abbreviated month (e.g "Nov") are recognized 
Sys.setlocale("LC_TIME", "en_GB.UTF-8") 
# or 
Sys.setlocale("LC_TIME", "C") 

#Then proceed as you intended 
x <- "Thu Nov 8 15:41:45 2012" 
strptime(x, "%a %b %d %H:%M:%S %Y") 
# [1] "2012-11-08 15:41:45" 

# Then set back to your old locale 
Sys.setlocale("LC_TIME", loc) 

我個人的語言環境，我可以重現你的錯誤：

Sys.setlocale("LC_TIME", loc) 
# [1] "fr_FR.UTF-8" 

strptime(var,"%a %b %d %H:%M:%S %Y") 
# [1] NA 

Answer 2

只是有同樣的問題瞎搞，結果發現此解決方案要更清潔，因爲不需要手動更改任何系統設置，因爲在lubridate包中有一個包裝函數執行此作業，並且您只需設置參數locale：

date <- c("23. juni 2014", "1. november 2014", "8. marts 2014", "16. juni 2014", "12. december 2014", "13. august 2014") 
df$date <- dmy(df$Date, locale = "Danish") 
[1] "2014-06-23" "2014-11-01" "2014-03-08" "2014-06-16" "2014-12-12" "2014-08-13"