[R] Working with data-frame

[Christofer Bogaso]

Hi again,

Let say, I have following data frame:


Dat <- structure(list(A1 = structure(c(3L, 3L, 1L, 3L, 3L, 3L, 3L, 2L,
3L, 3L, 1L, 2L, 3L, 2L, 1L, 1L, 3L, 3L, 2L, 3L, 2L, 2L, 3L, 3L,
3L, 2L, 3L, 1L, 1L, 3L), .Label = c("a", "b", "c"), class = "factor"),
    A2 = c(2, 3, 2, 1, 3, 3, 2, 2, 3, 1, 3, 1, 3, 3, 2, 2, 1,
    2, 1, 2, 1, 3, 3, 2, 1, 2, 3, 2, 2, 2), C1 = 1:30), .Names = c("A1",
"A2", "C1"), row.names = c(NA, -30L), class = "data.frame")


Now my goal is :
1: Find all possible unique combinations of column 'A1' & column 'A2'.
For example A1 = c, A2 = 2 is 1 unique combination.

2. For each such unique combination, calculate sum for 'A3'.

Is there any direct R function to achieve this faster way? I have very
large data-frame to handle with such calculation.

I tried with spilt() function. However it looks to me that, it can
split a data-frame w.r.t. only one column.

Thanks for your suggestion