我有时间数据，我想从黄昏中减去这些数据，我还有其他代码。要做到这一点，我首先需要将时间与最近的黄昏联系起来。我遇到的麻烦是在午夜后四舍五入时间，回到前一天的黄昏(参见：Df$time[2](
我在同一天成功地使用了多次带有period((的lubridate函数round_date，但对于凌晨时间，它只会恢复到当天的午夜。"；change_on_boundary"；帮助菜单中的参数似乎不再起作用。有人有别的办法吗？
*注：我知道tz变了，我不担心。这是这个问题的伪数据集。
Df<-data.frame(time = as.POSIXct(c("2020-12-29 21:02:23 UTC", "2020-12-15 00:48:21 UTC", "2020-12-09 21:55:52 UTC" ,"2020-12-09 18:40:06 UTC",
"2020-12-08 18:25:27 UTC" ,"2020-12-14 20:08:51 UTC", "2020-12-14 17:55:21 UTC","2020-12-05 23:53:36 UTC",
"2020-12-05 21:21:21 UTC", "2020-12-06 19:11:11 UTC", "2020-12-05 21:09:31 UTC", "2020-12-05 18:13:53 UTC",
"2020-12-15 20:36:56 UTC", "2020-12-26 06:00:00 UTC", "2020-12-16 00:40:46 UTC" ,"2020-12-26 05:34:42 UTC")))
Df$time
[1] "2020-12-29 21:02:23 EST" "2020-12-15 00:48:21 EST" "2020-12-09 21:55:52 EST" "2020-12-09 18:40:06 EST" "2020-12-08 18:25:27 EST"
[6] "2020-12-14 20:08:51 EST" "2020-12-14 17:55:21 EST" "2020-12-05 23:53:36 EST" "2020-12-05 21:21:21 EST" "2020-12-06 19:11:11 EST"
[11] "2020-12-05 21:09:31 EST" "2020-12-05 18:13:53 EST" "2020-12-15 20:36:56 EST" "2020-12-26 06:00:00 EST" "2020-12-16 00:40:46 EST"
[16] "2020-12-26 05:34:42 EST"
round_date(Df$time, unit = period(16, units = "hour"))
[1] "2020-12-29 16:00:00 EST" "2020-12-15 00:00:00 EST" "2020-12-09 16:00:00 EST" "2020-12-09 16:00:00 EST" "2020-12-08 16:00:00 EST"
[6] "2020-12-14 16:00:00 EST" "2020-12-14 16:00:00 EST" "2020-12-05 16:00:00 EST" "2020-12-05 16:00:00 EST" "2020-12-06 16:00:00 EST"
[11] "2020-12-05 16:00:00 EST" "2020-12-05 16:00:00 EST" "2020-12-15 16:00:00 EST" "2020-12-26 00:00:00 EST" "2020-12-16 00:00:00 EST"
[16] "2020-12-26 00:00:00 EST"
如果我正确理解问题，您希望每次四舍五入到最接近的16:00(下午4点(。正如您所发现的，lubridate::round_date()似乎在午夜四舍五入时停止。
举个例子，你可以找到哪些四舍五入的日期时间已经到达午夜，减去8个小时，得到前一天的16:00。
library(tidyverse)
library(lubridate)
Df %>%
tibble %>%
force_tz('UTC') %>%
mutate(
time_round = round_date(time, unit = period(16, units = 'hour')),
time_round_final = as_datetime(ifelse(hour(time_round) == 0, # if the hour is 0 (midnight), then...
time_round - hours(24 - 16), # we subtract 8 (24 - 16) hours, otherwise...
time_round)) # we keep the original rounded time
)
# A tibble: 16 x 3
# time time_round time_round_final
# <dttm> <dttm> <dttm>
# 1 2020-12-29 21:02:23 2020-12-29 16:00:00 2020-12-29 16:00:00
# 2 2020-12-15 00:48:21 2020-12-15 00:00:00 2020-12-14 16:00:00
# 3 2020-12-09 21:55:52 2020-12-09 16:00:00 2020-12-09 16:00:00
# 4 2020-12-09 18:40:06 2020-12-09 16:00:00 2020-12-09 16:00:00
# 5 2020-12-08 18:25:27 2020-12-08 16:00:00 2020-12-08 16:00:00
# 6 2020-12-14 20:08:51 2020-12-14 16:00:00 2020-12-14 16:00:00
# 7 2020-12-14 17:55:21 2020-12-14 16:00:00 2020-12-14 16:00:00
# 8 2020-12-05 23:53:36 2020-12-05 16:00:00 2020-12-05 16:00:00
# 9 2020-12-05 21:21:21 2020-12-05 16:00:00 2020-12-05 16:00:00
# 10 2020-12-06 19:11:11 2020-12-06 16:00:00 2020-12-06 16:00:00
# 11 2020-12-05 21:09:31 2020-12-05 16:00:00 2020-12-05 16:00:00
# 12 2020-12-05 18:13:53 2020-12-05 16:00:00 2020-12-05 16:00:00
# 13 2020-12-15 20:36:56 2020-12-15 16:00:00 2020-12-15 16:00:00
# 14 2020-12-26 06:00:00 2020-12-26 00:00:00 2020-12-25 16:00:00
# 15 2020-12-16 00:40:46 2020-12-16 00:00:00 2020-12-15 16:00:00
# 16 2020-12-26 05:34:42 2020-12-26 00:00:00 2020-12-25 16:00:00
我使用lubridate::force_tz()将时区应用于时间(它是空的(，否则as_datetime()似乎默认为UTC(它必须假设没有时区的时间是您的本地时区？(，并通过静默地更改(应用(时区来返回意外的时间。这可能是导致错误的常见原因。
当我们不强制时区时，我们可以观察到这一点(我在GMT+11(：
Df %>%
tibble %>%
# force_tz('UTC') %>%
mutate(
time_round = round_date(time, unit = period(16, units = 'hour')),
time_round_final = as_datetime(ifelse(hour(time_round) == 0, # if the hour is 0 (midnight), then...
time_round - hours(24 - 16), # we subtract 8 (24 - 16) hours, otherwise...
time_round)), # we keep the original rounded time
tz_1 = tz(time),
tz_2 = tz(time_round),
tz_3 = tz(time_round_final),
)
# # A tibble: 16 x 6
# time time_round time_round_final tz_1 tz_2 tz_3
# <dttm> <dttm> <dttm> <chr> <chr> <chr>
# 1 2020-12-29 21:02:23 2020-12-29 16:00:00 2020-12-29 05:00:00 "" "" UTC
# 2 2020-12-15 00:48:21 2020-12-15 00:00:00 2020-12-14 05:00:00 "" "" UTC
# 3 2020-12-09 21:55:52 2020-12-09 16:00:00 2020-12-09 05:00:00 "" "" UTC
# 4 2020-12-09 18:40:06 2020-12-09 16:00:00 2020-12-09 05:00:00 "" "" UTC
# 5 2020-12-08 18:25:27 2020-12-08 16:00:00 2020-12-08 05:00:00 "" "" UTC
# 6 2020-12-14 20:08:51 2020-12-14 16:00:00 2020-12-14 05:00:00 "" "" UTC
# 7 2020-12-14 17:55:21 2020-12-14 16:00:00 2020-12-14 05:00:00 "" "" UTC
# 8 2020-12-05 23:53:36 2020-12-05 16:00:00 2020-12-05 05:00:00 "" "" UTC
# 9 2020-12-05 21:21:21 2020-12-05 16:00:00 2020-12-05 05:00:00 "" "" UTC
# 10 2020-12-06 19:11:11 2020-12-06 16:00:00 2020-12-06 05:00:00 "" "" UTC
# 11 2020-12-05 21:09:31 2020-12-05 16:00:00 2020-12-05 05:00:00 "" "" UTC
# 12 2020-12-05 18:13:53 2020-12-05 16:00:00 2020-12-05 05:00:00 "" "" UTC
# 13 2020-12-15 20:36:56 2020-12-15 16:00:00 2020-12-15 05:00:00 "" "" UTC
# 14 2020-12-26 06:00:00 2020-12-26 00:00:00 2020-12-25 05:00:00 "" "" UTC
# 15 2020-12-16 00:40:46 2020-12-16 00:00:00 2020-12-15 05:00:00 "" "" UTC
# 16 2020-12-26 05:34:42 2020-12-26 00:00:00 2020-12-25 05:00:00 "" "" UTC