以R格式格式化日期（非标准格式）

对R或R中的格式化日期并不陌生，也不会问这个问题，但我有严重的奇怪行为，在过去的两个小时里，我还没有接近解决它

我有一个已导入的数据集，希望使用

as.POSIXct

格式化日期/时间列。日期是一种非标准格式，我已经应用了我所知道的正确格式。这是我遇到麻烦的一小部分数据。代码就在后面。问题是有4个NA从太平洋标准时间2015-03-08 02:00:00开始。有什么好处？这似乎完全是随机的，因为在其他任何55K观测中都没有发生

bad.Dates<-c("3/7/2015 14:15", "3/7/2015 14:30", "3/7/2015 14:45", "3/7/2015 15:00", 
         "3/7/2015 15:15", "3/7/2015 15:30", "3/7/2015 15:45", "3/7/2015 16:00", 
         "3/7/2015 16:15", "3/7/2015 16:30", "3/7/2015 16:45", "3/7/2015 17:00", 
         "3/7/2015 17:15", "3/7/2015 17:30", "3/7/2015 17:45", "3/7/2015 18:00", 
         "3/7/2015 18:15", "3/7/2015 18:30", "3/7/2015 18:45", "3/7/2015 19:00", 
         "3/7/2015 19:15", "3/7/2015 19:30", "3/7/2015 19:45", "3/7/2015 20:00", 
         "3/7/2015 20:15", "3/7/2015 20:30", "3/7/2015 20:45", "3/7/2015 21:00", 
         "3/7/2015 21:15", "3/7/2015 21:30", "3/7/2015 21:45", "3/7/2015 22:00", 
         "3/7/2015 22:15", "3/7/2015 22:30", "3/7/2015 22:45", "3/7/2015 23:00", 
         "3/7/2015 23:15", "3/7/2015 23:30", "3/7/2015 23:45", "3/8/2015 0:00", 
         "3/8/2015 0:15", "3/8/2015 0:30", "3/8/2015 0:45", "3/8/2015 1:00", 
         "3/8/2015 1:15", "3/8/2015 1:30", "3/8/2015 1:45", "3/8/2015 2:00", 
         "3/8/2015 2:15", "3/8/2015 2:30", "3/8/2015 2:45", "3/8/2015 3:00", 
         "3/8/2015 3:15", "3/8/2015 3:30", "3/8/2015 3:45", "3/8/2015 4:00", 
         "3/8/2015 4:15", "3/8/2015 4:30", "3/8/2015 4:45", "3/8/2015 5:00", 
         "3/8/2015 5:15", "3/8/2015 5:30", "3/8/2015 5:45", "3/8/2015 6:00", 
         "3/8/2015 6:15", "3/8/2015 6:30", "3/8/2015 6:45", "3/8/2015 7:00", 
         "3/8/2015 7:15", "3/8/2015 7:30", "3/8/2015 7:45", "3/8/2015 8:00", 
         "3/8/2015 8:15", "3/8/2015 8:30", "3/8/2015 8:45", "3/8/2015 9:00", 
         "3/8/2015 9:15", "3/8/2015 9:30", "3/8/2015 9:45", "3/8/2015 10:00", 
         "3/8/2015 10:15", "3/8/2015 10:30", "3/8/2015 10:45", "3/8/2015 11:00", 
         "3/8/2015 11:15", "3/8/2015 11:30", "3/8/2015 11:45", "3/8/2015 12:00", 
         "3/8/2015 12:15", "3/8/2015 12:30", "3/8/2015 12:45", "3/8/2015 13:00", 
         "3/8/2015 13:15", "3/8/2015 13:30", "3/8/2015 13:45", "3/8/2015 14:00", 
         "3/8/2015 14:15", "3/8/2015 14:30", "3/8/2015 14:45", "3/8/2015 15:00", 
         "3/8/2015 15:15") 

as.POSIXct(strptime(bad.Dates,"%m/%d/%Y %H:%M"))

---

bad.Dates要使此示例在任何位置都可重复/解决，请通过
tz=
明确指定时区：

bad.Dates <- c("3/8/2015 1:45", "3/8/2015 2:00", "3/8/2015 2:15",
               "3/8/2015 2:30", "3/8/2015 2:45", "3/8/2015 3:00")
as.POSIXct(bad.Dates, format="%m/%d/%Y %H:%M", tz="US/Pacific")

#[1] "2015-03-08 01:45:00 PST"
#[2] NA                       
#[3] NA                       
#[4] NA                       
#[5] NA                       
#[6] "2015-03-08 03:00:00 PDT"

这就是夏令时（PDT）开始的确切时间。因此，这一小时基本上没有时间了。幽灵般的“接得好，”理查德斯克里文说。柯蒂斯，停止战斗时间：）午饭后千万不要弄乱时间戳。在导入时间/日期数据时，通常最好使用“UTC”或“GMT”作为时区，除非您明确希望考虑时区和夏令时。顺便说一句。通过在as.POSIXct（）中指定
tz
解决了我的问题。现在，它在同一时区报告所有内容，没有NA。谢谢你的帮助@理查德斯克里文。
as.POSIXct(bad.Dates, format="%m/%d/%Y %H:%M", tz="UTC")
#[1] "2015-03-08 01:45:00 UTC"
#[2] "2015-03-08 02:00:00 UTC"
#[3] "2015-03-08 02:15:00 UTC"
#[4] "2015-03-08 02:30:00 UTC"
#[5] "2015-03-08 02:45:00 UTC"
#[6] "2015-03-08 03:00:00 UTC"