Shell Programming and Scripting

1  hi 
1  this
1  is
1  john
2  hello
3  test
3  case

     1  hi, this, is, john 
     2  hello 
     3  test, case

awk '{A[$1]=(A[$1]==""?$2:A[$1]","$2)}END{for(i in A) print i, A[i]}' file

awk '
{
        # Check if array indexed by 1st field (A[$1]) is null.
        # If yes, assign value = 2nd field ($2)
        # If no, assign value = previous value (A[$1]) comma (",") 2nd field ($2)
        A[$1] = A[$1] == "" ? $2 : A[$1] "," $2
}
        # END Block
END {
        # For each element in array
        # Print
        for (i in A) {
                print i, A[i]
        }
} ' file

[root@Imperfecto_1 test]# cat infile
1  hi a
1  this b
1  is
1  john
2  hello c d
3  test r
3  case

awk '{for(i=2;i<=NF;i++){A[$1]=(A[$1]?A[$1]","$i:$i)}}END{for(i in A){print i, A[i]}}' infile