I have two reference tables ,`ref1`

and `ref2`

. and a dataset, `df`

. All are `data.tables`

`ref1`

has variables `"V1"`

, `"V2"`

and `"x"`

`ref2`

has variables `"V1"`

and `"x"`

`df`

has variables `"V1"`

and `"V2"`

I want to extract the values of `"x"`

from `ref1`

and `ref2`

based on the appropriate values for `"V1"`

and `"V2"`

. There is no overlap between `"V1"`

values in `ref1`

and `ref2`

.

Some MWE data:

```
ref1 <- data.table(
V1 = c("a","a","a","b","b","b","e","e"),
V2 = c("1","2","3","4","5","6","10","11"),
x = c(43,66,12,19,92,30,44,56)
)
ref2 <- data.table(
V1 = c("c","d"),
x = c(100,200)
)
df <- data.table(
V1 = c("a","b","c","d","f"),
V2 = c("2","4","7","9","14")
)
target <- data.table(
V1 = c("a","b","c","d","f"),
V2 = c("2","4","7","9","14"),
x = c(66,19,100,200,NA)
)
```