Concatenating a column by a group in R

Question

Suppose I\'ve got this employee list:

 Dept Date      Name            
----- --------- --------------- 
   30 07-DEC-02 Raphaely        
   30 18-MAY-03 Khoo         


        

Answer 1

Or plyr:

gr<-read.csv("gr.csv")
require(plyr)
merge(gr,ddply(gr,.(Dept),summarise,Emp_List=paste0(Name,collapse="; ")),by="Dept")

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

Answer 2

You can use ave and 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