R的data.table找不到函数“。”

Question

I read that data.table understands the dot "." as an alias of "list". But:

> dt <- data.table(x = c(11, 22), y = c("f", "b"))
> dt
    x y
1: 11 f
2: 22 b
> dt[,.(y)]
Error in eval(expr, envir, enclos) : could not find function "."
>

Why is that?

Answer 1

According to the data.table New features on v.1.9.4 ( https://github.com/Rdatatable/data.table ),

.() can now be used in j and is identical to list(), for consistency with i.

So, it is better to install either v.1.9.4 version or the devel version from here