dev_null <- Sys.setlocale("LC_TIME", "english") weekdays( c(ISOdate(1970, 8, 28), ISOdate(2016, 9, 21))) # [1] "Friday" "Wednesday" weekdays( ISOdate(2000, 1, 1) + 0:6) # [1] "Saturday" "Saturday" "Saturday" "Saturday" "Saturday" "Saturday" "Saturday"