查找当前日期是否与上一个日期相同

Question

I have these date times:

library(lubridate)
my_date_times <- dmy_hm(c("17/05/16 23:49", "17/05/16 09:39", "08/08/16 23:21", "08/12/16 09:23", "26/02/17 08:03", "12/10/17 12:04", "12/10/17 10:03"))

I want to calculate whether a date is the same as the date in the previous row. If the current date is the same as the previous, then I would to add TRUE to both rows in the same_date variable. I'm not concerned if the two times do not match. Hopefully this code explains what I'm after.

same_date <- c(TRUE, TRUE, FALSE, FALSE, FALSE, TRUE, TRUE)
library(tibble)
df <- data_frame(my_date_times, same_date)
df 

# A tibble: 7 x 2
        my_date_times same_date
               <dttm>     <lgl>
1 2016-05-17 23:49:00      TRUE
2 2016-05-17 09:39:00      TRUE
3 2016-08-08 23:21:00     FALSE
4 2016-12-08 09:23:00     FALSE
5 2017-02-26 08:03:00     FALSE
6 2017-10-12 12:04:00      TRUE
7 2017-10-12 10:03:00      TRUE

Answer 1

The OP has requested to add TRUE to both rows if the current date is the same as the previous. This is why the diff() approach won't work here.

Instead, we can group by date and check whether the group consists only of one row or multiple rows.

library(data.table)
setDT(df)[, same_date  := .N > 1, by = as.Date(my_date_times)][]

  my_date_times same_date 1: 2016-05-17 23:49:00 TRUE 2: 2016-05-17 09:39:00 TRUE 3: 2016-08-08 23:21:00 FALSE 4: 2016-12-08 09:23:00 FALSE 5: 2017-02-26 08:03:00 FALSE 6: 2017-10-12 12:04:00 TRUE 7: 2017-10-12 10:03:00 TRUE