example.R

# The first function, `makeVector` creates a special "vector", which is
# really a list containing a function to
# 
# 1.  set the value of the vector
# 2.  get the value of the vector
# 3.  set the value of the mean
# 4.  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)
}



# 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 `get`s 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
}