R: how do you merge/combine two environments?

Question

This is a simple question but the answer is apparently not so simple... Is it possible to combine environments in R?

E1 = new.env()
E2 = new.env()
E1$x = 25
E2$y = 7

Ok, now I want an environment (say, E3) that has both x and y defined.

c(E1, E2)
#doesn't work
E3 = new.env(E1, E2)
#doesn't work

I have found other similar questions but they don't seem to work for me.

Use case: Maybe there's a reason this isn't easy...the reason I want to do this is thus: I use some functions to load up data. Previously, I've just loaded it into the global environment, but I now have many different functions loading different types of data (which I call variously as needed), and so I wanted to keep the loaded data a bit more compartmentalized. If I call 2 different loading functions E1=loadData1() and E2=loadData2(), and I now want to call a function that uses variables from both of these functions, I'd like to be able to say with(E1 & E2, someFunction()). Hence, merging my loaded environments seems appropriate.

So, what's the right way to merge them? And, as an aside, do you have a different suggestion for how to better accomplish what I'm doing, if merging environments is not the right way?

Answer 1

1) Make one environment the parent of the other and use with(child, ...) :

parent <- new.env(); parent$x <- 1
child <- new.env(parent = parent); child$y <- 2

with(child, x + y) # x comes from child and y from parent
## [1] 3

You can link as many environments as you like in as long a chain as necessary.

Note that if the child were initially created with no parent then you can add a parent later using:

parent.env(child) <- parent

Thus we define LoadData1 and LoadData2 as:

# define LoadData1 to have a parent argument
LoadData1 <- function(parent = emptyenv()) {
        # calculation of environment e goes here
        parent.env(e) <- parent
        e
}

# define LoadData2 to have a parent argument
LoadData2 <- function(parent = emptyenv()) {
        # calculation of environment e goes here
        parent.env(e) <- parent
        e
}

# run
e1 <- LoadData1()
e2 <- LoadData2(parent = e1)
with(e2, dataFrom1 + dataFrom2)

If you don't want to modify LoadData1 and LoadData2 from what they are now:

e1 <- LoadData1()
e2 <- LoadData2()
parent.env(e2) <- e1
with(e2, dataFrom1 + dataFrom2)

2) Convert to lists:

with(c(as.list(e1), as.list(e2)), somefunction())

ADDED Second approach.