strptime、as.POSIXct 和 as.Date 返回意外的 NA [英] strptime, as.POSIXct and as.Date return unexpected NA

问题描述

当我尝试解析以下格式的时间戳时:Thu Nov 8 15:41:45 2012"，仅返回 NA.

When I try to parse a timestamp in the following format: "Thu Nov 8 15:41:45 2012", only NA is returned.

我使用的是 Mac OS X、R 2.15.2 和 Rstudio 0.97.237.我的操作系统的语言是荷兰语:我想这与它有关.

I am using Mac OS X, R 2.15.2 and Rstudio 0.97.237. The language of my OS is Dutch: I presume this has something to do with it.

当我尝试 strptime 时，返回 NA:

When I try strptime, NA is returned:

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

as.POSIXct 也不起作用:

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

我也在上面的字符串上尝试了 as.Date 但没有 %H:%M:%S 组件:

I also tried as.Date on the string above but without %H:%M:%S components:

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

知道我可能做错了什么吗?

Any ideas what I could be doing wrong?

推荐答案

我认为正如您所猜测的那样，strptime 由于您的语言环境而无法解析您的日期时间字符串.您的字符串包含缩写的工作日 (%a) 和缩写的月份名称 (%b).?strptime 中描述了这些时间规范:

I think it is exactly as you guessed, strptime fails to parse your date-time string because of your locales. Your string contains both abbreviated weekday (%a) and abbreviated month name (%b). These time specifications are described in ?strptime:

详情

%a:在当前语言环境中的缩写工作日名称 平台

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

%b:本平台当前语言环境中的月份缩写.

"请注意，缩写名称是特定于平台的(尽管标准指定在 C 语言环境中，它们必须是前三个英文名称的大写字母:"

"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:"

如果您想使用，了解缩写是必不可少的%a、%b 或 %h 作为输入格式的一部分:参见示例如何检查."

"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."

另见

[...] locales 查询或设置区域设置.

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

locales 的问题也与 as.POSIXct、as.POSIXlt 和 as.Date 相关.

The issue of locales is relevant also for as.POSIXct, as.POSIXlt and as.Date.

来自?as.POSIXct:

详情

如果指定了format，记住一些格式规范是特定于区域设置的，您可能需要设置LC_TIME 通过 Sys.setlocale 适当地分类.这个最常影响%b、%B(月份名称)和%p(AM/PM)的使用.

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).

从 ?as.Date:

详情

使用特定于语言环境的字符串之间的转换在适当和可用的情况下.这会影响日期的名称和几个月.

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

<小时>

因此，如果字符串中的工作日和月份名称与当前语言环境中的不同，strptime、as.POSIXct 和 as.Date 无法正确解析字符串并返回 NA.

---

Thus, if weekdays and month names in the string differ from those in the current locale, strptime, as.POSIXct and as.Date fail to parse the string correctly and NA is returned.

但是，您可以通过更改locales 来解决此问题:

However, you may solve this issue by changing the locales:

# 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) 

使用我的个人语言环境，我可以重现您的错误:

With my personal locale I can reproduce your error:

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

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

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