Id        begin_date          end_date
   2312561   2016-04-22          2016-06-27
   6429734   2015-03-19          2015-05-22

"Id","begin_date","end_date"
    2312561,2016-04-22,2016-06-27
    6429734,2015-03-19,2015-05-22

TestId        = df$Id
    start_date    = df$begin_date
    end_date      = df$end_date

    header  = paste0("Id",",", "begin_date",",","end_date",collapse = "','")
    testdt  = paste0(TestId,",", paste0(start_date),",",paste0(end_date),collapse = "','")

    allpaste = c(header, testdt)

[1] "Id,begin_date,end_date"                                  "2312561,2016-04-22,2016-06-27','6429734,2015-03-19,2015-05-22"

"Id","begin_date","end_date"
    2312561,2016-04-22,2016-06-27
    6429734,2015-03-19,2015-05-22