a <- data.frame("TYPE" = c("A", "A", "B", "B",
                           "C", "C", "C", "C",
                           "D", "D", "D", "D"),
                "DATE" = c("4/20/2018 11:47",
                           "4/25/2018 7:21",
                           "4/15/2018 6:11",
                           "4/19/2018 4:22",
                           "4/15/2018 17:46",
                           "4/16/2018 11:59",
                           "4/20/2018 7:50",
                           "4/26/2018 2:55",
                           "4/27/2018 11:46",
                           "4/27/2018 13:03",
                           "4/20/2018 7:31",
                           "4/22/2018 9:45"))