R - 迄今为止的午夜 POSIXct

Question

If I have midnight (or even around midnight posixct) date like this

> as.POSIXct("2020-01-01 00:00:00")
[1] "2020-01-01 CET"

But if I transfer it to the date I get one day before this date

> as.Date(as.POSIXct("2020-01-01 00:00:00"))
[1] "2019-12-31"

In case that hour is lets say 8am etc, as.Date works properly. How can I get 2020-01-01 date for my example where hour is midnight?

Answer 1

You need to specify the timezone again.

As you can see in ?as.Date :

## S3 method for class 'POSIXct'

as.Date(x, tz = "UTC", ...)

The function defaults to UTC.

as.Date(as.POSIXct("2020-01-01 00:00:00",tz="CET"),tz="CET")
#[1] "2020-01-01"

as.Date(as.POSIXct("2020-01-01 00:00:00",tz="CET"))
#[1] "2019-12-31"