cachemean.R

## Creates a special "vector", which is really a list containing a function to
## - set the value of the vector
## - get the value of the vector
## - set the value of the mean
## - get the value of the mean
makeVector <- function(x = numeric()) {
  m <- NULL
  set <- function(y) {
    x <<- y
    m <<- NULL
  }
  get <- function() x
  setmean <- function(mean) m <<- mean
  getmean <- function() m
  list(set = set, get = get,
       setmean = setmean,
       getmean = getmean)
}

## In this example we introduce the <<- operator which can be used to assign 
## a value to an object in an environment that is different from the current 
## environment. Below are two functions that are used to create a special 
## object that stores a numeric vector and caches its mean.

##  The following function calculates the mean of the special "vector" created 
## with the above function. However, it first checks to see if the mean has 
## already been calculated. 
##
## If so, it gets the mean from the cache and skips the computation. Otherwise, 
## it calculates the mean of the data and sets the value of the mean in the 
## cache via the setmean function.
cachemean <- function(x, ...) {
  m <- x$getmean()
  if(!is.null(m)) {
    message("getting cached data")
    return(m)
  }
  data <- x$get()
  m <- mean(data, ...)
  x$setmean(m)
  m
}