当我尝试将POSIXct日期时间强制转换为Dateusing时as.Date，似乎返回了错误的日期。
我怀疑这与时区有关。我在中尝试了该tz参数as.Date，但未给出预期的日期。
# POSIXct returns day of month 24
data$Time[3]
# [1] "2020-03-24 00:02:00 IST"
class(data$Time[3])
# [1] "POSIXct" "POSIXt"
# coerce to Date, returns 23
as.Date(data$Time[3])
# [1] "2020-03-23"
# try the time zone argument, without luck
as.Date(data$Time[3], tz = "IST")
# [1] "2020-03-23"
# Warning message:
# In as.POSIXlt.POSIXct(x, tz = tz) : unknown timezone 'IST'
Sys.timezone()
# [1] "Asia/Calcutta"
有什么想法可能出什么问题吗？
最后使用注释中的设置，我们可以使用以下任意一种：
# same date as print(x) shows
as.Date(as.character(x))
## [1] "2020-03-24"
# use the time zone stored in x (or system time zone if that is "")
as.Date(x, tz = attr(x, "tzone"))
## [1] "2020-03-24"
# use system time zone
as.Date(x, tz = "")
## [1] "2020-03-24"
# use system time zone
as.Date(x, tz = Sys.timezone())
## [1] "2020-03-24"
# use indicated time zone
as.Date(x, tz = "Asia/Calcutta")
## [1] "2020-03-24"
我们假设此设置。
Sys.setenv(TZ = "Asia/Calcutta")
x <- structure(1584988320, class = c("POSIXct", "POSIXt"), tzone = "")
R.version.string
## [1] "R version 4.0.2 Patched (2020-06-24 r78745)"
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我来说两句