How can I create a day number variable in R based on dates? - r

Question

I want to create a variable with the number of the day a participant took a survey (first day, second day, thirds day, etc.)
The issue is that there are participants that took the survey after midnight.
For example, this is what it looks like:
Id
date
1
08/03/2020 08:17
1
08/03/2020 12:01
1
08/04/2020 15:08
1
08/04/2020 22:16
2
07/03/2020 08:10
2
07/03/2020 12:03
2
07/04/2020 15:07
2
07/05/2020 00:16
3
08/22/2020 09:17
3
08/23/2020 11:04
3
08/24/2020 00:01
4
10/03/2020 08:37
4
10/03/2020 11:13
4
10/04/2020 15:20
4
10/04/2020 23:05
This is what I want:
Id
date
day
1
08/03/2020 08:17
1
1
08/03/2020 12:01
1
1
08/04/2020 15:08
2
1
08/04/2020 22:16
2
2
07/03/2020 08:10
1
2
07/03/2020 12:03
1
2
07/04/2020 15:07
2
2
07/05/2020 00:16
2
3
08/22/2020 09:17
1
3
08/23/2020 11:04
2
3
08/24/2020 00:01
2
4
10/03/2020 08:37
1
4
10/03/2020 11:13
1
4
10/04/2020 15:20
2
4
10/04/2020 23:05
2
How can I create the day variable taking into consideration participants that who took the survey after midnight still belong to the previous day?
I tried the codes here. But I have issues with participants taking surveys after midnight.

Answer 1

Please check the below code
code
data2 <- data %>%
mutate(date2 = as.Date(date, format = "%m/%d/%Y %H:%M")) %>%
group_by(id) %>%
mutate(row = row_number(),
date3 = as.Date(ifelse(row == 1, date2, NA), origin = "1970-01-01")) %>%
fill(date3) %>%
ungroup() %>%
mutate(diff = as.numeric(date2 - date3 + 1)) %>%
select(-date2, -date3, -row)
output
#> id date diff
#> 1 1 08/03/2020 08:17 1
#> 2 1 08/03/2020 12:01 1
#> 3 1 08/04/2020 15:08 2
#> 4 1 08/04/2020 22:16 2
#> 5 2 07/03/2020 08:10 1
#> 6 2 07/03/2020 12:03 1
#> 7 2 07/04/2020 15:07 2
#> 8 2 07/05/2020 00:16 3

Answer 2

Here is one approach that explicitly will show dates considered. First, would make sure your date is in POSIXct format as suggested in comments (if not done already). Then, if the hour is less than 2 (midnight to 2 AM) subtract 1 from the date so the survey_date reflects the day before. If the hour is not less than 2, just keep the date. The timezone tz argument is set to "" to avoid confusion or uncertainty. Finally, after grouping by Id, subtract each survey_date from the first survey_date to get number of days since first survey. You can use as.numeric to make this column numeric if desired.
Note: if you want to just note consecutive days taken the survey (and ignore gaps in days between surveys) you can substitute for the last line:
mutate(day = cumsum(survey_date != lag(survey_date, default = first(survey_date))) + 1)
This will increase day by 1 every new survey_date found for a given Id.
library(tidyverse)
library(lubridate)
df %>%
mutate(date = as.POSIXct(date, format = "%m/%d/%Y %H:%M", tz = "")) %>%
mutate(survey_date = if_else(hour(date) < 2,
as.Date(date, format = "%Y-%m-%d", tz = "") - 1,
as.Date(date, format = "%Y-%m-%d", tz = ""))) %>%
group_by(Id) %>%
mutate(day = survey_date - first(survey_date) + 1)
Output
Id date survey_date day
<int> <dttm> <date> <drtn>
1 1 2020-08-03 08:17:00 2020-08-03 1 days
2 1 2020-08-03 12:01:00 2020-08-03 1 days
3 1 2020-08-04 15:08:00 2020-08-04 2 days
4 1 2020-08-04 22:16:00 2020-08-04 2 days
5 2 2020-07-03 08:10:00 2020-07-03 1 days
6 2 2020-07-03 12:03:00 2020-07-03 1 days
7 2 2020-07-04 15:07:00 2020-07-04 2 days
8 2 2020-07-05 00:16:00 2020-07-04 2 days
9 3 2020-08-22 09:17:00 2020-08-22 1 days
10 3 2020-08-23 11:04:00 2020-08-23 2 days
11 3 2020-08-24 00:01:00 2020-08-23 2 days
12 4 2020-10-03 08:37:00 2020-10-03 1 days
13 4 2020-10-03 11:13:00 2020-10-03 1 days
14 4 2020-10-04 15:20:00 2020-10-04 2 days
15 4 2020-10-04 23:05:00 2020-10-04 2 days