使用dplyr基于POSIXct日期和时间大于日期时间的子集数据帧 [英] Subset dataframe based on POSIXct date and time greater than datetime using dplyr

问题描述

我不确定选择日期时间作为POSIXct格式会出什么问题.我已经阅读了一些有关基于as.Date设置数据框子集的评论，并且可以使它正常工作.我也读过很多文章，建议过滤POSIXct格式应该可以，但是由于某种原因，我无法使它起作用.

I am not sure what is going wrong with selecting date times as a POSIXct format. I have read several comments on subsetting a dataframe based on as.Date and I can get that to work without an issue. I have also read many posts suggesting that filtering POSIXct formats should work, but for some reason I cannot get it to work.

示例数据框:

library(lubridate)
library(dplyr)

date_test <- seq(ymd_hms('2016-07-01 00:00:00'),ymd_hms('2016-08-01 00:00:00'), by = '15 min')
date_test <- data.frame(date_test)
date_test$datetime <- date_test$date_test
date_test <- select(date_test, -date_test)

我检查了它是否为POSIXct格式，然后尝试了几种方式对大于2016-07-01 01:15:00的数据框进行子集化.但是输出不会显示小于2016-07-01 01:15:00被删除的日期时间.很抱歉，如果有人问过这个问题，我找不到它，但是我已经寻找并试图使它生效.我将UTC用作时区以避免夏令时问题，所以这里不是问题-除非过滤器需要它.

I checked that it is in POSIXct format and then tried several ways to subset the dataframe greater than 2016-07-01 01:15:00. However the output never shows the date times less than 2016-07-01 01:15:00 being removed. I am sorry if this has been asked somewhere and I cannot find it but I have looked and tried to get this to work. I am using UTC as the timezone to avoid daylight savings time issues so that is not the issue here - unless the filter requires it.

class(date_test$datetime)

date_test <- date_test %>% filter(datetime > '2016-07-01 01:15:00')

date_test <- date_test %>% 
  filter(datetime > as.POSIXct("2016-07-01 00:15"))

date_test <- subset(date_test, datetime > as.POSIXct('2016-07-01 01:15:00')) 

现在，如果我使用以下方法进行过滤:

Now if I filter using:

date_test <- date_test %>% 
  filter(datetime > as.POSIXct("2016-07-10 01:15:00"))

输出是很奇怪的，因为时间错了一天?

the output is very strange with a day behind and the wrong time?

2016-07-09 13:30:00
2016-07-09 13:45:00
2016-07-09 14:00:00
2016-07-09 14:15:00
2016-07-09 14:30:00

如果有帮助，我将Mac OS Sierra与R Studio版本1.0.143和R You Stupid Darkness，DPLYR 0.5和Lubridate 1.6一起使用

If it helps I am using MAC OS Sierra with R Studio Version 1.0.143 and R You Stupid Darkness, DPLYR 0.5 and Lubridate 1.6

推荐答案

ymd_hms默认在"UTC"时区使用POSIXct次-as.POSIXct使用系统时区(例如-澳大利亚对我而言)-您需要按照评论中Dave的建议，始终使用ymd_hms或更改为"UTC"时区.

ymd_hms uses POSIXct times in "UTC" timezone by default - as.POSIXct uses the system timezone (e.g. - Australia for me) - you need to consistently use ymd_hms or change to the "UTC" timezone as per Dave's suggestion in the comments.

例如:这些示例有效:

date_test <- seq(ymd_hms('2016-07-01 00:30:00'),ymd_hms('2016-07-01 01:30:00'), by = '15 min')
date_test <- data.frame(datetime=date_test)
date_test

#             datetime
#1 2016-07-01 00:30:00
#2 2016-07-01 00:45:00
#3 2016-07-01 01:00:00
#4 2016-07-01 01:15:00
#5 2016-07-01 01:30:00

date_test %>% 
  filter(datetime > as.POSIXct("2016-07-01 01:00:00", tz="UTC"))

date_test %>% 
  filter(datetime > ymd_hms("2016-07-01 01:00:00"))

#             datetime
#1 2016-07-01 01:15:00
#2 2016-07-01 01:30:00

这篇关于使用dplyr基于POSIXct日期和时间大于日期时间的子集数据帧的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！