Sammanfoga en kolumn med en grupp i R

Du kan använda ave och paste :

within(mydf, {
  Emp_list <- ave(Name, Dept, FUN = function(x) paste(x, collapse = "; "))
})
#   Dept      Date      Name          Emp_list
# 1    30 07-DEC-02  Raphaely    Raphaely; Khoo
# 2    30 18-MAY-03      Khoo    Raphaely; Khoo
# 3    40 07-JUN-02    Mavris            Mavris
# 4    50 01-MAY-03  Kaufling  Kaufling; Ladwig
# 5    50 14-JUL-03    Ladwig  Kaufling; Ladwig
# 6    70 07-JUN-02      Baer              Baer
# 7    90 13-JAN-01   De Haan     De Haan; King
# 8    90 17-JUN-03      King     De Haan; King
# 9   100 16-AUG-02    Faviet Faviet; Greenberg
# 10  100 17-AUG-02 Greenberg Faviet; Greenberg
# 11  110 07-JUN-02     Gietz    Gietz; Higgins
# 12  110 07-JUN-02   Higgins    Gietz; Higgins