The Big R-Book

♣5♣Lexical Scoping and Environments

5.1 Environments in R

Environments can be thought of as a set of existing or declared objects (functions, variables, etc.). When we start R, it will create an environment before the command prompt is available to the user.

The top-level environment is the R command prompt. This is the “global environment” and known as R_GlobalEnv and can be accessed as .GlobalEnv.

global environment

R_GlobalEnv

As mentioned earlier, the function ls() shows which variables and functions are defined in the current environment. The function environment() will tell us which environment is the current one.

environment()

environment() # get the environment 
## <environment: R_GlobalEnv> 

rm(list=ls()) # clear the environment
ls()          # list all objects 
## character(0) 

a <- “a” 
f <- function (x) print(x) 
ls()          # note that x is not part of.GlobalEnv 
## [1] “a” “f” 

When a function starts to be executed this will create a new environment that is subordonated to the environment that calls the function.

# f 
# Multiple actions and side effects to illustrate environments 
# Arguments: 
#   x -- single type 
f <- function(x){ 
       # define a local function g() within f() 
       g <- function(y){ 
             b <- “local variable in g()” 
             print(” -- function g() -- “) 
             print(environment()) 
             print(ls()) 
             print(paste(“b is”, b)) 
             print(paste(“c is”, c)) 
             }

       # actions in function f: 
       a <<- ‘new value for a, also in Global_env’ 
       x <- ‘new value for x’ 
       b <- d # d is taken from the environment ...