How to get environment of a variable in R

问题

I was wondering if there is anyway to get the environment of a declared variable. Say I already have declared a variable to an environment and want to use that variable's environment to declare a few more variables. Something like getEnv("variable")

回答1:

Refer to: http://adv-r.had.co.nz/Environments.html#env-basics

library(pryr)
x <- 5
where("x")
#> <environment: R_GlobalEnv>
where("mean")
#> <environment: base>

The where function is described in the above website. It only finds the first environment the variable appears in, but could easily be modified to find all.

回答2:

You can get all objects in your workspace with ls(), so you can then check which of those are environments:

envirs <- ls()[sapply(ls(), function(x) is.environment(get(x)))]

I need to use get() there because ls() returns character names of objects rather than the objects themselves. Now given some object x, we want to find which environments it exists in. All we need to do is iterate through each environment in envirs, and check if they contain whatever object we're looking for. Something along the lines of (checking for a variable x):

sapply(envirs, function(e) 'x' %in% ls(envir=get(e)))

Here's a function to do all this:

getEnv <- function(x) {
  xobj <- deparse(substitute(x))
  gobjects <- ls(envir=.GlobalEnv)
  envirs <- gobjects[sapply(gobjects, function(x) is.environment(get(x)))]
  envirs <- c('.GlobalEnv', envirs)
  xin <- sapply(envirs, function(e) xobj %in% ls(envir=get(e)))
  envirs[xin] 
}

This is more or less the same as what I did outside the function. gobjects reads from ls(), this time explicitly checking the global environment .GlobalEnv, since it is now within a function.

envirs is the same as before, except now it will check .GlobalEnv as well. xin is storing the names of which environments x was found in. The line:

xobj <- deparse(substitute(x))

Allows object to be tested without quotes e.g. getEnv(x) versus getEnv('x'). That's a matter of preference though, you can change it to accept characters instead.

Here's a few tests.

x1 <- 1
getEnv(x1)
# ".GlobalEnv"

x2 <- 2.1
e2 <- new.env()
assign('x2', 2.2, e2)
getEnv(x2)
# ".GlobalEnv" "e2" 

e3 <- new.env()
assign('x3', 3, e3)
getEnv(x3)
# "e3"

This only checks environments created within .GlobalEnv. I'm sure you can work out how to extend it to search across more environments though if you need.

I'm surprised there isn't some in-built function for this. Or maybe there is and I don't know about it. I've never actually needed to do anything like this before so maybe it's not actually surprising.

回答3:

How about this:

getEnvOf <- function(what, which=rev(sys.parents())) {
  for (frame in which)
    if (exists(what, frame=frame, inherits=FALSE)) 
      return(sys.frame(frame))
  return(NULL)
}

Then we can:

x <- 1
getEnvOf("x")
# <environment: R_GlobalEnv>

getEnvOf("y")
# NULL

f <- function() getEnvOf("x")
f()
# <environment: R_GlobalEnv>

g <- function() { x <- 2; getEnvOf("x") }
g()
# <environment: 0x114c26518>

来源：https://stackoverflow.com/questions/16583211/how-to-get-environment-of-a-variable-in-r

标签

variables

scope

env