With this dummy dataframe:
library(tibble)
library(dplyr)
tibble(Date = as.POSIXct(c(1601848800, 1601852400, 1601856000,
1601859600, 1601863200), origin = "1970-01-01")) %>%
mutate(ISOweek = format(as.Date(.$Date), "%V"))
I get this result which baffles me:
Date ISOweek
<dttm> <chr>
1 2020-10-05 00:00:00 40
2 2020-10-05 01:00:00 40
3 2020-10-05 02:00:00 41
4 2020-10-05 03:00:00 41
5 2020-10-05 04:00:00 41
I am getting the Date variable from a csv file, so maybe I am converting from character to POSIXct in an unproper manner.
as.POSIXct uses your local timezone and as.Date uses UTC timezone. If you specify the timezone in as.POSIXct the output will be clear to you. Also adding a date column should help clarify the result.
library(dplyr)
tibble(Date = as.POSIXct(c(1601848800, 1601852400, 1601856000, 1601859600,
1601863200), origin = "1970-01-01", tz = 'UTC')) %>%
mutate(date = as.Date(Date),
ISOweek = format(date, "%V"))
# Date date ISOweek
# <dttm> <date> <chr>
#1 2020-10-04 22:00:00 2020-10-04 40
#2 2020-10-04 23:00:00 2020-10-04 40
#3 2020-10-05 00:00:00 2020-10-05 41
#4 2020-10-05 01:00:00 2020-10-05 41
#5 2020-10-05 02:00:00 2020-10-05 41