R - 给定 Olson 时区的 UTC 到本地时间

Question

我有 1974-2013 年的时间序列数据，其中有一列用于 datetimeUTC (YYYY-MM-DD hh:mm +0000)，一列用于奥尔森格式的时区(例如加拿大/太平洋、加拿大/东部) .我可以像这样将整个 UTCdatetime 列转换为通用时区:

dataset$datetimeEST <- strptime(
  dataset$datetimeUTC, format="%Y-%m-%d %H:%M:%S%z", tz="Canada/Eastern"
)  

如何将 datetimeUTC 转换为 datetimeLOCAL，给定每一行中相应的时区？

让我稍微备份一下。我有来自全国(6 个时区)的数据，这些数据以 1974-2013 年的 ISO8601 格式表示。时间戳全年采用本地标准时间(即，即使该地区的民用时间遵守夏令时，夏令时也会被忽略)。我需要进行日期时间计算，这在 UTC 时间中可能是最安全的，所以这很容易。但是，我还需要提取特定民用时间段的数据，同时考虑 DST，并为该子集数据进行计算和绘图(例如，所有 6 个时区的位置的高峰时段的所有数据)。

我在下面计算的 datetimeCLOCKTIME 似乎在做我想要的绘图，但在进行日期时间计算时给出了错误的答案，因为它在没有实际转换时间的情况下将日期时间存储在我本地机器的时区中。 @thelatemail 提供的解决方案是我正在寻找的解决方案，但我无法在 Windows 中使用 2012 年的测试数据集(见下文)。另外，我正在使用转换为 POXITlt 的 strptime，他的解决方案是在 POXITct 中。我是 R 的新手，所以任何帮助都将不胜感激。

测试数据集:

    dataset <- data.frame (timestampISO8601 = c("2012-04-25T22:00:00-08:00","2012-04-25T22:15:00-08:00","2012-04-25T22:30:00-08:00","2012-04-25T22:45:00-08:00","2012-04-25T23:00:00-08:00","2012-04-25T23:15:00-08:00","2012-04-25T23:30:00-08:00","2012-04-25T23:45:00-08:00","2012-04-26T00:00:00-08:00","2012-04-26T00:15:00-08:00","2012-04-26T00:30:00-08:00","2012-04-26T00:45:00-08:00","2012-04-26T01:00:00-08:00","2012-04-26T01:15:00-08:00","2012-04-26T01:30:00-08:00","2012-04-26T01:45:00-08:00","2012-04-26T02:00:00-08:00","2012-04-25T22:00:00-03:30","2012-04-25T22:15:00-03:30","2012-04-25T22:30:00-03:30","2012-04-25T22:45:00-03:30","2012-04-25T23:00:00-03:30","2012-04-25T23:15:00-03:30","2012-04-25T23:30:00-03:30","2012-04-25T23:45:00-03:30","2012-04-26T00:00:00-03:30","2012-04-26T00:15:00-03:30","2012-04-26T00:30:00-03:30","2012-04-26T00:45:00-03:30","2012-04-26T01:00:00-03:30","2012-04-26T01:15:00-03:30","2012-04-26T01:30:00-03:30","2012-04-26T01:45:00-03:30","2012-04-26T02:00:00-03:30"), olson = c("Canada/Pacific","Canada/Pacific","Canada/Pacific","Canada/Pacific","Canada/Pacific","Canada/Pacific","Canada/Pacific","Canada/Pacific","Canada/Pacific","Canada/Pacific","Canada/Pacific","Canada/Pacific","Canada/Pacific","Canada/Pacific","Canada/Pacific","Canada/Pacific","Canada/Pacific","Canada/Newfoundland","Canada/Newfoundland","Canada/Newfoundland","Canada/Newfoundland","Canada/Newfoundland","Canada/Newfoundland","Canada/Newfoundland","Canada/Newfoundland","Canada/Newfoundland","Canada/Newfoundland","Canada/Newfoundland","Canada/Newfoundland","Canada/Newfoundland","Canada/Newfoundland","Canada/Newfoundland","Canada/Newfoundland","Canada/Newfoundland"), value = c(0,0,1,2,5,11,17,19,20,19,17,11,5,2,1,0,0,-3,-3,-2,-1,2,8,14,16,17,16,14,8,2,-1,-2,-3,-3), stringsAsFactors=FALSE)

从 UTC 偏移量中删除“:”。 (R 期望 UTC 偏移量的格式为 nnnn):

    dataset$timestampR<- paste(substr(dataset$timestampISO8601,1,22),substr(dataset$timestampISO8601,24,25),sep="")

当转换为 UTC 时间时，R 默认为 UTC 偏移量为 -ve，使时间戳中的 -ve 偏移量为正值:

    dataset$datetimeUTC <- strptime(dataset$timestampR, format="%Y-%m-%dT%H:%M:%S%z", tz="UTC")

像这样转换为机器时间时，R 读取输入时间并将其转换为本地机器时区的时间 - 在我的例子中，这是加拿大/东部:

    dataset$datetimeMACHINE <- strptime(dataset$timestampR, format="%Y-%m-%dT%H:%M:%S%z")

当像这样转换为 CLOCKTIME 时间时，R 读取输入时间并分配本地机器的时区(当前在我的机器上为 EDT)，而不进行任何时间转换:

    dataset$datetimeCLOCKTIME <- strptime(dataset$timestampR,format="%Y-%m-%dT%H:%M:%S")

查看数据集的结构:

    str(dataset)  

绘图行为不同

    library(ggplot2)
    qplot(data=dataset,x=datetimeUTC,y=value)
    qplot(data=dataset,x=datetimeMACHINE,y=value)
    qplot(data=dataset,x=datetimeCLOCKTIME,y=value)

计算结果不同。 datetimeCLOCKTIME 的计算结果不正确:

    range (dataset$datetimeUTC)
    range (dataset$datetimeMACHINE)
    range (dataset$datetimeCLOCKTIME)

    dataset$datetimeUTC[34] - dataset$datetimeUTC[1]
    dataset$datetimeMACHINE[34] - dataset$datetimeMACHINE[1]
    dataset$datetimeCLOCKTIME[34] - dataset$datetimeCLOCKTIME[1]

Answer 1

您可以来回设置格式以获得字符格式的本地时间表示。例如:

dataset <- data.frame(
  datetimeUTC=c("2014-01-01 00:00 +0000","2014-01-01 00:00 +0000"),
  olson=c("Canada/Eastern", "Canada/Pacific"),
  stringsAsFactors=FALSE
)

#             datetimeUTC          olson
#1 2014-01-01 00:00 +0000 Canada/Eastern
#2 2014-01-01 00:00 +0000 Canada/Pacific

dataset$localtime <- with(dataset, 
     mapply(function(dt,ol) format(
              as.POSIXct(dt,"%Y-%m-%d %H:%M %z",tz=ol),
              "%Y-%m-%d %H:%M %z"), 
              datetimeUTC, olson
            )
     )

#             datetimeUTC          olson              localtime
#1 2014-01-01 00:00 +0000 Canada/Eastern 2013-12-31 19:00 -0500
#2 2014-01-01 00:00 +0000 Canada/Pacific 2013-12-31 16:00 -0800