将unix秒（毫秒）转换为POSIXct / POSIXlt [英] Converting unix seconds in milliseconds to POSIXct/POSIXlt

问题描述

为什么在R中将unix时间戳转换为datetime对象时，我会看到一个区别？

Why do I see a difference when I convert a unix timestamp to datetime object in R?

> as.POSIXlt(1268736919, origin="1970-01-01", tz="America/New_York")
[1] "2010-03-16 06:55:19 EDT"

> as.POSIXct(1268736919, origin="1970-01-01", tz="America/New_York")
[1] "2010-03-16 11:55:19 EDT"

POSIXlt的结果实际上是正确的。

The result from POSIXlt is actually correct.

另外，是否有

谢谢

推荐答案

p>帮助页面实际上提示了一个区别：

The help page actually hints at a difference:

Value:

     ‘as.POSIXct’ and ‘as.POSIXlt’ return an object of the appropriate
     class.  If ‘tz’ was specified, ‘as.POSIXlt’ will give an
     appropriate ‘"tzone"’ attribute.

这个东西很精致 - 我认为有一个隐含的TZ转换发生在 as.POSIXct 。考虑

This stuff is finicky -- I think there is an implicit TZ conversion happening for as.POSIXct. Consider that

R> print(as.numeric(as.POSIXct(as.POSIXlt(1268736919, 
                               origin="1970-01-01"))), digits=10)
[1] 1268736919
R> print(as.numeric(as.POSIXct(1268736919, origin="1970-01-01")), digits=10)
[1] 1268758519

第二个（使用 as.POSIXct ）不返回原始输入。不幸的是，Brian D. Ripley似乎是唯一拥有所有细节的人。

the second one (using as.POSIXct) does not return the original input. Unfortunately, Brian D. Ripley seems to be the only human having all the details here.

最后，你不能没有起源。但是你可以定义使用时代作为起源的包装（如这里），或者使用2000-01-01或...只要保持一致。

Lastly, you can't do it without the origin. But you could define wrappers that use the epoch as origin (as here) or use 2000-01-01 or ... Just keep it consistent.

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