Dear all,

I'm trying to use data.table to summarise a table and merge it to another table. Here is what I would like to do, but by using data.table() in a proper way.

library(data.table)
tab1 <- data.table(ID = 11:20, A = rnorm(10), D = 1:10, key = "ID")
tab2 <- data.table(ID2 = 1:10, D = rep(1:5, 2), B = rnorm(10), key = "ID2")
junk <- aggregate(tab2[, B], by = list(D = tab2[, D]), FUN = sum)
merge(tab1, junk, by = "D", all.x = TRUE)

This my attempt using data.table()

junk <- tab2[, mean(B), by = D]
tab1[junk]

Best regards,

Thierry



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