df <- data.frame("6Jun06" = c(4, 5, 9),
    "13Jun06" = c(4, 5, 9),
    "20Jun06" = c(4, 5, 9),
    "03Jul16" = c(1, 2, 3),
    "09Jul16" = c(1, 2, 3),
    "01Aug16" = c(1, 2, 5))

X6.Jun.06 X13.Jun.06 X20.Jun.06 Jun.Sum X03.Jul.16 X09.Jul.16 Jul.Sum X01.Aug.16 Aug.Sum
1         4          4          4     Sum          1          1     Sum          1     Sum
2         5          5          5     Sum          2          2     Sum          2     Sum
3         9          9          9     Sum          3          3     Sum          5     Sum