5  Environments

Environments consist of a frame, or collection of named objects, and a pointer to an enclosing environment. The most common example is the frame of variables local to a function call; its enclosure is the environment where the function was defined (unless changed subsequently). The enclosing environment is distinguished from the parent frame: the latter (returned by parent.frame) refers to the environment of the caller of a function.

Recommended readings:

5.1 .GlobalEnv

The global environment is the workspace where you interact with R. When you type an expression in the console, it is evaluated in the global environment. When you create a variable or a function, it is stored in the global environment. The global environment is also the top-level environment of the search path.

f <- function(x) { #"top level function"
  return(x * 2)
}

##-- all five give the same:
environment()   # current environment
environment(f)

.GlobalEnv
globalenv()
sys.frame()

identical(environment(), globalenv())

is.environment(.GlobalEnv) # TRUE

When a function is called, the R interpreter searches the implementation of the function along the search path

search()

Once a new package is attached, it is added to the top of the search path, just behind GlobalEnv:

library("ggplot2")
search()

image source

5.2 Create an environment

  • new.env, creates a new environment
  • ls, returns a vector of all object (function and variable) names in an environment.
  • rm, removes objects from a specified environment
e <- new.env()
parent.env(e)

e$x <- 5
assign("y", 3, envir = e)
ls(e)
is.null(e$x)
is.null(e$y)
is.null(e$z)

e$y <- NULL
ls(e)

rm(y, envir = e)
ls(e)

rm(list = ls()) # clear all in current environment

ls gives information about what’s available in a package

ls("package:graphics")

5.3 Parent

Different environments can be linked together by setting the parent environment of one environment to another. When looking for an object, R will first look in the current environment, and if it doesn’t find it, it will look in the parent environment, and so on until it reaches the empty environment.

ftl <- function(x) { #"top level function"
  return(x * 2)
}

e1 <- new.env()
e2 <- new.env(parent = e1)
assign("a", 3, envir = e1)
ls(e1)
ls(e2)
exists("a", envir = e2)   # this succeeds by inheritance
exists("a", envir = e2, inherits = FALSE)
is.null(e2$a)
exists("ftl", envir = e2) # this succeeds by inheritance
exists("ftl", envir = e2, inherits = FALSE)

5.4 .with

a <- 10
e <- new.env()
e$a <- 5
r <- with(e, {
  print(paste("a =", a, "(with-e)"))
  a <- 55
  a + 500
})
print(paste("e$a =", e$a))
print(paste("a =", a))
print(paste("r =", r))
  • with can be used with both environments and list data structures that we will see in the next lecture
x <- 11
l <- list(x = 1, y = 2)
with(l, {
  print(x)
})
print(x)