Mutate time (HH:MM:SS) to date (YYYY-MM-DD) accounting for midnight in R

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I am trying to convert time in HH:MM:SS to date as YYYY-MM-DD in R accounting for midnight.

Time spans from morning in day 1 to morning in day 2, but I wanted to create a new column with a specific date in which time after midnight would indicate a new day. Here's an example:

Current data:

structure(list(ID = c("ID_002", "ID_002", "ID_002", "ID_002", 
"ID_002", "ID_002", "ID_002", "ID_002", "ID_002", "ID_002", "ID_002", 
"ID_002", "ID_002", "ID_002", "ID_002", "ID_002", "ID_002", "ID_002", 
"ID_002", "ID_002", "ID_002", "ID_002", "ID_002", "ID_002", "ID_002", 
"ID_002", "ID_002", "ID_002", "ID_002"), Time = c("05:01:00", 
"06:01:00", "07:01:00", "08:01:00", "09:01:00", "10:01:00", "11:01:00", 
"12:01:00", "13:01:00", "14:01:00", "15:01:00", "16:01:00", "17:01:00", 
"18:01:00", "19:01:00", "20:01:00", "21:01:00", "22:01:00", "23:01:00", 
"00:01:00", "01:01:00", "02:01:00", "03:01:00", "04:01:00", "05:01:00", 
"06:01:00", "07:01:00", "08:01:00", "09:01:00")), row.names = c(NA, 
29L), class = "data.frame")

Desired output:

ID      Time Date
ID_001  08:01:00    2021-01-20
ID_001  10:01:00    2021-01-20
ID_001  12:01:00    2021-01-20
ID_001  14:01:00    2021-01-20
ID_001  16:01:00    2021-01-20
ID_001  18:01:00    2021-01-20
ID_001  20:01:00    2021-01-20
ID_001  22:01:00    2021-01-20
ID_001  00:01:00    2021-01-21
ID_001  02:01:00    2021-01-21
ID_001  04:01:00    2021-01-21
ID_001  06:01:00    2021-01-21
ID_001  08:01:00    2021-01-21

Thanks for your help!

r date datetime
2 Answers

A combination of dplyr and lubridate is a possible way to get what you want.

First determine if there is a new day by checking if the difference in lagged times is negative. If so add a day to the first day. Then use a cumsum to add all the days to the start date.

library(dplyr)
library(lubridate)
first_date <- ymd("2021-01-20")

df1 %>% 
  mutate(add_a_day = if_else(hms(Time) - lag(hms(Time), default = hms("00:00:00")) < 0, 1, 0),
         Date = first_date + cumsum(add_a_day)
         ) %>% 
  select(-add_a_day)

       ID     Time       Date
1  ID_002 05:01:00 2021-01-20
2  ID_002 06:01:00 2021-01-20
3  ID_002 07:01:00 2021-01-20
4  ID_002 08:01:00 2021-01-20
5  ID_002 09:01:00 2021-01-20
6  ID_002 10:01:00 2021-01-20
7  ID_002 11:01:00 2021-01-20
8  ID_002 12:01:00 2021-01-20
9  ID_002 13:01:00 2021-01-20
10 ID_002 14:01:00 2021-01-20
11 ID_002 15:01:00 2021-01-20
12 ID_002 16:01:00 2021-01-20
13 ID_002 17:01:00 2021-01-20
14 ID_002 18:01:00 2021-01-20
15 ID_002 19:01:00 2021-01-20
16 ID_002 20:01:00 2021-01-20
17 ID_002 21:01:00 2021-01-20
18 ID_002 22:01:00 2021-01-20
19 ID_002 23:01:00 2021-01-20
20 ID_002 00:01:00 2021-01-21
21 ID_002 01:01:00 2021-01-21
22 ID_002 02:01:00 2021-01-21
23 ID_002 03:01:00 2021-01-21
24 ID_002 04:01:00 2021-01-21
25 ID_002 05:01:00 2021-01-21
26 ID_002 06:01:00 2021-01-21
27 ID_002 07:01:00 2021-01-21
28 ID_002 08:01:00 2021-01-21
29 ID_002 09:01:00 2021-01-21
user_49851760

Will this do?

library(tidyverse)
starting_date <- as.Date('2021-01-20')
library(lubridate)

df %>% 
  mutate(Date = starting_date + cumsum(lag(hms(Time), default = hms('00:00:01')) > hms(Time) ))

#>        ID     Time       Date
#> 1  ID_002 05:01:00 2021-01-20
#> 2  ID_002 06:01:00 2021-01-20
#> 3  ID_002 07:01:00 2021-01-20
#> 4  ID_002 08:01:00 2021-01-20
#> 5  ID_002 09:01:00 2021-01-20
#> 6  ID_002 10:01:00 2021-01-20
#> 7  ID_002 11:01:00 2021-01-20
#> 8  ID_002 12:01:00 2021-01-20
#> 9  ID_002 13:01:00 2021-01-20
#> 10 ID_002 14:01:00 2021-01-20
#> 11 ID_002 15:01:00 2021-01-20
#> 12 ID_002 16:01:00 2021-01-20
#> 13 ID_002 17:01:00 2021-01-20
#> 14 ID_002 18:01:00 2021-01-20
#> 15 ID_002 19:01:00 2021-01-20
#> 16 ID_002 20:01:00 2021-01-20
#> 17 ID_002 21:01:00 2021-01-20
#> 18 ID_002 22:01:00 2021-01-20
#> 19 ID_002 23:01:00 2021-01-20
#> 20 ID_002 00:01:00 2021-01-21
#> 21 ID_002 01:01:00 2021-01-21
#> 22 ID_002 02:01:00 2021-01-21
#> 23 ID_002 03:01:00 2021-01-21
#> 24 ID_002 04:01:00 2021-01-21
#> 25 ID_002 05:01:00 2021-01-21
#> 26 ID_002 06:01:00 2021-01-21
#> 27 ID_002 07:01:00 2021-01-21
#> 28 ID_002 08:01:00 2021-01-21
#> 29 ID_002 09:01:00 2021-01-21

Created on 2021-11-27 by the reprex package (v2.0.0)

user_28848590
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