In R, how to make the variables inside a function available to the lower level function inside this function?(with, attach, environment)
Solution 1
(1) Pass caller's environment. You can explicitly pass the parent environment and index into it. Try this:
f2a <- function(P, env = parent.frame()) {
env$calls <- env$calls + 1
print(env$calls)
return(P + env$c + env$d)
}
a <- 1
b <- 2
# same as f1 except f2 removed and call to f2 replaced with call to f2a
f1a <- function(){
c <- 3
d <- 4
calls <- 0
v <- vector()
for(i in 1:10){
v[i] <- f2a(P=0)
c <- c+1
d <- d+1
}
return(v)
}
f1a()
(2) Reset called function's environment We can reset the environment of f2b
in f1b
as shown here:
f2b <- function(P) {
calls <<- calls + 1
print(calls)
return(P + c + d)
}
a <- 1
b <- 2
# same as f1 except f2 removed, call to f2 replaced with call to f2b
# and line marked ## at the beginning is new
f1b <- function(){
environment(f2b) <- environment() ##
c <- 3
d <- 4
calls <- 0
v <- vector()
for(i in 1:10){
v[i] <- f2b(P=0)
c <- c+1
d <- d+1
}
return(v)
}
f1b()
(3) Macro using eval.parent(substitute(...)) Yet another approach is to define a macro-like construct which effectively injects the body of f2c
inline into f1c1
. Here f2c
is the same as f2b
except for the calls <- calls + 1
line (no <<-
needed) and the wrapping of the entire body in eval.parent(substitute({...}))
. f1c
is the same as f1a
except the call to f2a
is replaced with a call to f2c
.
f2c <- function(P) eval.parent(substitute({
calls <- calls + 1
print(calls)
return(P + c + d)
}))
a <- 1
b <- 2
f1c <- function(){
c <- 3
d <- 4
calls <- 0
v <- vector()
for(i in 1:10){
v[i] <- f2c(P=0)
c <- c+1
d <- d+1
}
return(v)
}
f1c()
(4) defmacro This is almost the same as the the last solution except it uses defmacro
in the gtools package to define the macro rather than doing it ourself. (Also see the Rcmdr package for another defmacro version.) Because of the way defmacro
works we must also pass calls
but since it's a macro and not a function this just tells it to substitute calls
in and is not the same as passing calls
to a function.
library(gtools)
f2d <- defmacro(P, calls, expr = {
calls <- calls + 1
print(calls)
return(P + c + d)
})
a <- 1
b <- 2
f1d <- function(){
c <- 3
d <- 4
calls <- 0
v <- vector()
for(i in 1:10){
v[i] <- f2d(P=0, calls)
c <- c+1
d <- d+1
}
return(v)
}
f1d()
Solution 2
In general, I would say that any variable that is needed inside a function should be passed on through its arguments. In addition, if its value is needed later you pass it back from the function. Not doing this can quite quickly lead to strange results, e.g. what if there are multiple functions defining a variable x
, which one should be used. If the amount of variables is larger, you create a custom data structure for it, e.g. putting them into a named list.
Solution 3
One could also use a function that redefines other functions in the specified environment.
test_var <- "global"
get_test_var <- function(){
return(test_var)
}
some_function <- function(){
test_var <- "local"
return(get_test_var())
}
some_function() # Returns "global". Not what we want here...
# ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
some_function2 <- function(){
test_var <- "local"
# define function locally
get_test_var2 <- function(){
return(test_var)
}
return(get_test_var2())
}
some_function2() # Returns "local", but 'get_test_var2' can't be used in other places.
# ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
add_function_to_envir <- function(my_function_name, to_envir) {
script_text <- capture.output(eval(parse(text = my_function_name)))
script_text[1] <- paste0(my_function_name, " <- ", script_text[1])
eval(parse(text = script_text), envir = to_envir)
}
some_function3 <- function(){
test_var <- "local"
add_function_to_envir("get_test_var", environment())
return(get_test_var())
}
some_function3() # Returns "local" and we can use 'get_test_var' from anywhere.
Here add_function_to_envir(my_function_name, to_envir)
captures the script of the function, parses and reevaluates it in the new environment.
Note: the name of the function for my_function_name
needs to be in quotes.
Comments
-
Zhenglei almost 4 years
Update 2 @G. Grothendieck posted two approaches. The second one is changing the function environment inside a function. This solves my problem of too many coding replicates. I am not sure if this is a good method to pass through the CRAN check when making my scripts into a package. I will update again when I have some conclusions.
Update
I am trying to pass a lot of input argument variables to
f2
and do not want to index every variable inside the function asenv$c, env$d, env$calls
, that is why I tried to usewith
inf5
andf6
(a modifiedf2
). However,assign
does not work withwith
inside the{}
, movingassign
outsidewith
will do the job but in my real case I have a fewassign
s inside thewith
expressions which I do not know how to move them out of thewith
function easily.Here is an example:
## In the <environment: R_GlobalEnv> a <- 1 b <- 2 f1 <- function(){ c <- 3 d <- 4 f2 <- function(P){ assign("calls", calls+1, inherits=TRUE) print(calls) return(P+c+d) } calls <- 0 v <- vector() for(i in 1:10){ v[i] <- f2(P=0) c <- c+1 d <- d+1 } return(v) } f1()
Function
f2
is insidef1
, whenf2
is called, it looks for variablescalls,c,d
in the environmentenvironment(f1)
. This is what I wanted.However, when I want to use
f2
also in the other functions, I will define this function in the Global environment instead, call itf4
.f4 <- function(P){ assign("calls", calls+1, inherits=TRUE) print(calls) return(P+c+d) }
This won't work, because it will look for
calls,c,d
in the Global environment instead of inside a function where the function is called. For example:f3 <- function(){ c <- 3 d <- 4 calls <- 0 v <- vector() for(i in 1:10){ v[i] <- f4(P=0) ## or replace here with f5(P=0) c <- c+1 d <- d+1 } return(v) } f3()
The safe way should be define
calls,c,d
in the input arguments off4
and then pass these parameters intof4
. However, in my case, there are too many variables to be passed into this functionf4
and it would be better that I can pass it as an environment and tellf4
do not look in the Global environment(environment(f4)
), only look inside theenvironment
whenf3
is called.The way I solve it now is to use the environment as a list and use the
with
function.f5 <- function(P,liste){ with(liste,{ assign("calls", calls+1, inherits=TRUE) print(calls) return(P+c+d) } ) } f3 <- function(){ c <- 3 d <- 4 calls <- 0 v <- vector() for(i in 1:10){ v[i] <- f5(P=0,as.list(environment())) ## or replace here with f5(P=0) c <- c+1 d <- d+1 } return(v) } f3()
However, now
assign("calls", calls+1, inherits=TRUE)
does not work as it should be sinceassign
does not modify the original object. The variablecalls
is connected to an optimization function where the objective function isf5
. That is the reason I useassign
instead of passingcalls
as an input arguments. Usingattach
is also not clear to me. Here is my way to correct theassign
issue:f7 <- function(P,calls,liste){ ##calls <<- calls+1 ##browser() assign("calls", calls+1, inherits=TRUE,envir = sys.frame(-1)) print(calls) with(liste,{ print(paste('with the listed envrionment, calls=',calls)) return(P+c+d) } ) } ######## ################## f8 <- function(){ c <- 3 d <- 4 calls <- 0 v <- vector() for(i in 1:10){ ##browser() ##v[i] <- f4(P=0) ## or replace here with f5(P=0) v[i] <- f7(P=0,calls,liste=as.list(environment())) c <- c+1 d <- d+1 } f7(P=0,calls,liste=as.list(environment())) print(paste('final call number',calls)) return(v) } f8()
I am not sure how this should be done in R. Am I on the right direction, especially when passing through the CRAN check? Anyone has some hints on this?
-
Zhenglei over 11 yearsI agree with you @Paul in general . I am trying to make my codes an R package but cannot pass through the CRAN check easily with many warnings like global variable bindings. There is many repeated code because the
f2
is defined inside a function and I want to use it in another new function. I realize that copy paste it is not a good option and can cause problems in later steps. I also want to reduce the effort because I don't want to change the already existing scrips too much. That's why I try to pass the environment instead of define a new data structure. -
Zhenglei over 11 yearsThis gives the result I want but I did not write clearly my request. In fact, I want to avoid to index all the variables passing into
f2
, i.e, not writingenv$
, that is why I tried to usewith
. I want to be able to modify the outsidecalls
insidef2
but not changing the other variables in the current environment. I will update the question. -
Zhenglei over 11 yearsIt looks like just what I need. I will test it with my real case and update later. Thank you very much for the help!