A Little About Dates in R Before we launch into any analysis that contains dates, we should know a few important nuggets about how R handles date-like objects. There are 3 date/time classes are built in to R - Date - POSIXct - POSIXlt Base R First, base R can read a string of text and convert it to a date class. To help it read the date, you must tell R what date format your character string should expect.