Retrieving day and time (in minutes) from character timestamp

Question

I have a timestamp in character in the following format with a suffixed Z:

"2022-03-01T00:00:00Z"

I wanted to retrieve the day in numbers and the time in minutes (should return 0 from the above example).

I tried the execute the following code but my output only retrieve the year-month-day and not the time format.

time_stamp <- as.POSIXct(participant1_data$timestamp[1], format="%Y-%m-%dT%H:%M")
str(time_stamp)


Output: POSIXct[1:1], format: "2022-03-01"

Is there anything wrong with the code that does not retrieve the time format?

Answer 1

1. As noted in comments, use tz="UTC", otherwise the "Z" == UTC (zulu) information gets lost, also see this answer.

2. If time is exactly midnight, the output is omitted.

as.POSIXct('2022-03-01T00:00:00Z', tz="UTC", "%Y-%m-%dT%H:%M:%OSZ")
# [1] "2022-03-01 UTC"

as.POSIXct('2022-03-01T11:11:11Z', tz="UTC", "%Y-%m-%dT%H:%M:%OSZ")
# [1] "2022-03-01 11:11:11 UTC"

3. You have now read in the time correctly and got "POSIXct" class. To achieve a different output from it, you need to format it to character with the desired format using strftime which allows to specify the correct timezone tz=, e.g. "CET".

strftime(as.POSIXct('2022-03-01T00:00:00Z', tz="UTC", "%Y-%m-%dT%H:%M:%OSZ"),
         '%F %R', tz='CET')
# [1] "2022-03-01 01:00"

strftime(as.POSIXct('2022-03-01T11:11:11Z', tz="UTC", "%Y-%m-%dT%H:%M:%OSZ"),
         '%F %R', tz='CET')
# [1] "2022-03-01 12:11"

Or if I understand "day in numbers and the time in minutes correctly, you maybe want this:

strftime(as.POSIXct('2022-03-01T11:11:11Z', tz="UTC", "%Y-%m-%dT%H:%M:%OSZ"),
         '%d %M', tz='CET')
# [1] "01 11"

Type help('strftime') or short ?strftime into the R console and read the help page for possible in/output options.