data.table query
On Fri, Dec 3, 2010 at 6:38 PM, Santosh Srinivas
<santosh.srinivas at gmail.com> wrote:
Hello Group, I need a modification in the data.table example to get my intended result shown below ... is there a more simple way! dt <- data.table(A = rep(1:3, each=4), B = rep(1:4, each=3), C = rep(1:2, 6)) dt[, transform(.SD,D=mean(A)), by="B"] The result I want is below ... which is probably long winded! data.table(unique(as.data.frame(dt[, transform(.SD,D=mean(A)), by="B"][,list(B,D)]))) ? ? B ? ? ? ?D [1,] 1 1.000000 [2,] 2 1.666667 [3,] 3 2.333333 [4,] 4 3.000000
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