Working with date and timestamp in R language
There are three basic date and time classes: Date, POSIXct and POSIXlt
Class Date handles dates without times.
Date and POSIXct are internally stored as number of seconds from January 1, 1970.
POSIXlt stores dates and times as a list of components: second, minute, hour, day, month, year, time zone etc.
POSIXct (calendar time) and POSIXlt (local time) represent dates and times.