Is there a way to subset a data table by the result of a grouped aggregation
without adding an interim column to the table? For example, if I want to select
all rows for which the group mean value of x is less than 10, I can do the
following:
data <- data.table(x = 1:20, g = rep(c("a", "b"), each = 10))
data[, mean.x := mean(x), by = .(g)]
data[mean.x < 10,]
But I'm not really interested in "mean.x". Can I do the same thing without
adding it to the table?
Thanks.
- Elliot
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