Dates and Times.md

Dates and Times

Converting a character string to a time

> as.POSIXct("1985-05-08 14:00:00", "UTC")
[1] "1985-05-08 14:00:00 UTC"

or

> strptime("2017-02-09", format="%Y-%m-%d", tz = "UTC")
[1] "2017-02-09 UTC"

Converting a Unix timestamp to a time

Using as.Date:

> as.Date(1453725582 / 86400, origin = "1970-01-01")
[1] "2016-01-25"

Using as.POSIXct:

> as.POSIXct(1479740483, "UTC", origin = "1970-01-01")
[1] "2016-11-21 15:01:23 UTC"

Formatting a date

When the date is the character class:

> as.Date("2016-01-29 15:23:26", format="%Y-%m-%d")
[1] "2016-01-29"

When the date is the Date class or POSIXlt:

> format(as.Date(1453725582 / 86400, origin = "1970-01-01"), "%Y")
[1] "2016"

Determining how much time is between two dates

Use difftime - note that the older time is the second argument:

> start <- as.POSIXct("1985-05-08 14:00:00", "UTC")
> difftime(Sys.time(), start)
Time difference of 11521.04 days

Or as an integer:

> as.integer(difftime(Sys.time(), start))
[1] 11521

difftime defaults to days, but you can specify other units too:

> as.integer(difftime(Sys.time(), start, units = c("hours")))
[1] 276505