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         


        

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.