[datatable-help] basic data.table query

[Santosh Srinivas]

Someone in r-help recommended me to post the question in this group . TIA

 

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

Thank you.

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