Implemented matrix cache functions

John McGrath · John McGrath · commit ed678619232c · 2014-05-22T22:32:58.000-07:00
diff --git a/cachematrix.R b/cachematrix.R
@@ -1,15 +1,56 @@
-## Put comments here that give an overall description of what your
-## functions do
-
-## Write a short comment describing this function
+## This excercise contains two functions:
+## - makeCacheMatrix(x) caches the inverse of a matrix object,
+## - cacheSolve, which does the inverting and commits it to the cache.
 
+## This function takes a square matrix as a parameter, and returns a special "matrix" object that can cache its inverse.
 makeCacheMatrix <- function(x = matrix()) {
-
+  i <- NULL
+  
+  # takes a matix, and sets it as the value to calculate the inverse of
+  set <- function(y) {
+    x <<- y
+    i <<- NULL
+  }
+  
+  # returns the value to calculate the inverse of
+  get <- function() x
+  
+  # caches the inverst of the matrix
+  setinverse <- function(inverse) i <<- inverse
+  
+  # gets the cached value of the matrix, or NULL if it hasn't been cached yet
+  getinverse <- function() i
+  
+  # return a list with all the function in the object
+  list(set = set, get = get,
+       setinverse = setinverse,
+       getinverse = getinverse)
 }
 
 
-## Write a short comment describing this function
-
+## This function takes a makeCacheMatrix object.
+## The first time it's run, it calculates the inverse of that matrix with `solve`,
+## caches it, and returns it. If run again it returns that cached value.
 cacheSolve <- function(x, ...) {
-        ## Return a matrix that is the inverse of 'x'
+  
+  # Get the cached inverse from the makeCacheMatrix object
+  inverse <- x$getinverse()
+  
+  # If it's not null, return it, along with a message that you've gotten it from the cache
+  if(!is.null(inverse)) {
+    message("getting cached data")
+    return(inverse)
+  }
+  
+  # If we've gotten here, it wasn't cached, so get the matrix...
+  data <- x$get()
+  
+  # calculate its inverse...
+  inverse <- solve(data)
+  
+  # cache it...
+  x$setinverse(inverse)
+  
+  # and return it.
+  inverse
 }
