R中从POSIXct到Date的日期转换 [英] Date conversion from POSIXct to Date in R

问题描述

谁能告诉我为什么 R 在下面给出这样的结果:

can anyone tell me why R give such outcome below:

> as.POSIXct("2013-01-01 08:00")
[1] "2013-01-01 08:00:00 HKT"
> as.Date(as.POSIXct("2013-01-01 08:00"))
[1] "2013-01-01"
> as.POSIXct("2013-01-01 07:00")
[1] "2013-01-01 07:00:00 HKT"
> as.Date(as.POSIXct("2013-01-01 07:00"))
[1] "2012-12-31"

2013-01-01 将POSIXct 转换为Date 后不应该是2013-01-01 for 2013-01-01 07:00，有什么办法可以把截止时间从08:00改成00:00?

Shouldn't it be 2013-01-01 after converting POSIXct to Date for 2013-01-01 07:00, is there any way to change the cutoff from 08:00 to 00:00?

我发现以下内容可以解决我的问题，但方式不太好

I found the following can fix my problem, but in a less neat way

> as.Date(as.character(as.POSIXct("2013-01-01 07:00")))
[1] "2013-01-01"

推荐答案

这里的问题是时区 - 您可以看到您在 "HKT" 中.试试:

The problem here is timezones - you can see you're in "HKT". Try:

as.Date(as.POSIXct("2013-01-01 07:00", 'GMT'))
[1] "2013-01-01"

从 ?as.Date():

["POSIXct" is] 通过忽略午夜后的时间转换为天在指定时区的时间表示中，默认UTC

["POSIXct" is] converted to days by ignoring the time after midnight in the representation of the time in specified timezone, default UTC

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