cachematrix.R

cachematrix.R

@@ -1,15 +1,39 @@
-## Put comments here that give an overall description of what your
-## functions do
-
-## Write a short comment describing this function
-
 makeCacheMatrix <- function(x = matrix()) {
-
+  inv <- NULL  # this will store the inverse later
+
+  # 1. set() - set a new matrix and reset cached inverse
+  set <- function(y) {
+    x <<- y
+    inv <<- NULL
+  }
+
+  # 2. get() - get the current matrix
+  get <- function() x
+
+  # 3. setinverse() - store (cache) the inverse
+  setinverse <- function(inverse) inv <<- inverse
+
+  # 4. getinverse() - get the cached inverse
+  getinverse <- function() inv
+
+  # return a list of all 4 functions
+  list(set = set, get = get,
+       setinverse = setinverse,
+       getinverse = getinverse)
 }
 
-
-## Write a short comment describing this function
-
 cacheSolve <- function(x, ...) {
-        ## Return a matrix that is the inverse of 'x'
+  inv <- x$getinverse()  # check if inverse already cached
+
+  if (!is.null(inv)) {   # if yes, just return it
+    message("getting cached data")
+    return(inv)
+  }
+
+  # if not cached, calculate it
+  data <- x$get()
+  inv <- solve(data, ...)  # compute inverse
+  x$setinverse(inv)        # store inverse in cache
+
+  inv                      # return the result
 }