Working solution for PA2 with a test suite

Author: kmayer

cachematrix-test.R

@@ -0,0 +1,23 @@
+library("testthat")
+context("Calculate the inverse of a square matrix")
+
+testData <- function(x = matrix()) {
+  inverseX <- solve(x)
+  y <- makeCacheMatrix(x)  
+  list(x = x, inverseX = inverseX, y = y)
+}
+
+test_that("match the example output for this function", {
+  data <- testData(matrix(1:4, 2, 2))
+  expect_equal(cacheSolve(data$y), data$inverseX)
+  expect_equal(data$y$getHits(), 0)
+  expect_equal(cacheSolve(data$y), data$inverseX)
+  expect_equal(data$y$getHits(), 1)
+  
+  data <- testData(matrix(rnorm(16 * 16), 16, 16))
+  expect_equal(cacheSolve(data$y), data$inverseX)
+  expect_equal(cacheSolve(data$y), data$inverseX)
+  expect_equal(cacheSolve(data$y), data$inverseX)
+  expect_equal(data$y$getHits(), 2)
+})
+

cachematrix.R

@@ -1,15 +1,58 @@
-## Put comments here that give an overall description of what your
-## functions do
-
-## Write a short comment describing this function
-
-makeCacheMatrix <- function(x = matrix()) {
+## Calculate the Inverse of a Matrix
+## Provide a caching mechanism to reduce computation costs
 
+## `makeCacheMatrix`: Create a matrix with a memoizable solution
+##
+## args:: *theMatrix* is just a matrix
+##
+## methods::
+## $setMatrix - will (re)set the original matrix and clear the memoized solution
+## $getMatrix - returns the original matrix
+## $setSolution - sets the calculated solution
+## $getSolution - returns the calculated solution
+## $cacheHit - increment the cache hit counter
+## $getHits - returns the number of times there was a cache "hit"
+##            and we skipped recomputing the solution
+makeCacheMatrix <- function(theMatrix = matrix()) {
+  cachedSolution <- NULL
+  cacheHits <- 0
+  
+  setMatrix <- function(newMatrix) {
+    theMatrix <<- newMatrix
+    cachedSolution <<- NULL
+    cacheHits <<- 0
+  }
+  getMatrix <- function() theMatrix
+  
+  setSolution <- function(solution) cachedSolution <<- solution
+  
+  getSolution <- function() cachedSolution
+  
+  cacheHit <- function() {
+    cacheHits <<- cacheHits + 1
+  }
+  
+  getHits <- function() cacheHits
+  
+  list(setMatrix = setMatrix, getMatrix = getMatrix,
+       setSolution = setSolution, getSolution = getSolution,
+       cacheHit = cacheHit, getHits = getHits)
 }
 
 
-## Write a short comment describing this function
-
+## `cacheSolve`: Return a matrix that is the inverse of 'x'
+##
+## args:: *x* was created using `makeCacheMatrix`
+##        The original matrix must be solveable, or else an error will raise
+##
+## Use the cached results if possible
 cacheSolve <- function(x, ...) {
-        ## Return a matrix that is the inverse of 'x'
+  solution <- x$getSolution()
+  if(!is.null(solution)) {
+    x$cacheHit()
+    return(solution)
+  }
+  solution <- solve(x$getMatrix(), ...)
+  x$setSolution(solution)
+  solution
 }