Working with data-frame
Christopher: If I understand correctly, see ?ave, or ?tapply, depending on what form you want to be returned. The trick is to first paste the columns together on whose unique you want to split to form a singtl factor. e.g. of the form lapply(split(yourcolumn,paste0(...)),FUN= sum) However, the above functions already have this "built" in, so you don't need to do this explicitly, although my impression is that it may be a tad more efficient to do it the long way. But don't quote me on this! Cheers, Bert Bert Gunter Genentech Nonclinical Biostatistics (650) 467-7374 "Data is not information. Information is not knowledge. And knowledge is certainly not wisdom." Clifford Stoll On Sun, Nov 9, 2014 at 11:58 AM, Christofer Bogaso
<bogaso.christofer at gmail.com> wrote:
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
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