Cut out scope between key and data.frame for data.table

When using data.table for searching, it is very fast. There is one behavior that does not work with my current workflow, and I am sure there is a better way and I am missing it. The behavior is to change in place, even if the key was taken from the parent data.frame

, data.table will act on the parent in data.frame

ways that may not always be desired.

Here's an example, as I am missing the language to express it correctly:

library(data.table)

set.seed(123)
N <- 100

key <- data.frame(x = sample.int(N, N), y = 1:N, z = 1:N)
key$w <- key$x
head(key)
##    x y z  w
## 1 29 1 1 29
## 2 79 2 2 79
## 3 41 3 3 41
## 4 86 4 4 86
## 5 91 5 5 91
## 6  5 6 6  5

set.seed(1)
terms <- data.frame(z = sample.int(2 * N, 1e2, replace = TRUE))
subkey <- key[c("x", "y")]

setDT(subkey)
setDT(terms)

setkey(subkey, x)
subkey[terms][[2]]

head(key)
##   x  y z w
## 1 1 74 1 1
## 2 2 35 2 2
## 3 3 51 3 3
## 4 4 18 4 4
## 5 5  6 5 5
## 6 6 54 6 6

      

        
        
        
      

    

Note that the order is key

affected by usage data.table

even though it was not used in the search?

I know I data.table

avoid making copies, but is there a way to cut this link to key

and force the data.table

act on subkey

without changing key

?