Completed assignment 2 solution

cachematrix.R

@@ -1,15 +1,53 @@
-## Put comments here that give an overall description of what your
-## functions do
+# Takes a matrix (a grid of numbers) as input.
+# Creates a little toolbox with four tools:
+#         
+# set           :  Updates the matrix with a new one and clears the old inverse.
+# get           : Shows you the matrix.
+# setinverse    : Saves the inverse in the memory box.
+# getinverse    : Lets you peek at the saved inverse.
+# 
+# 
+# Uses a list to hold these tools so you can call them anytime.
+
+makeCacheMatrix <- function(x = matrix()) {  # x is your matrix, starts empty
+        inv <- NULL  # This is where we’ll save the inverse, starts as nothing
+        set <- function(y) {  # Change the matrix to a new one (y)
+                x <<- y    # Save the new matrix in the magic box
+                inv <<- NULL  # Clear the old inverse
+        }
+        get <- function() x  # Show me the matrix
+        setinverse <- function(inverse) inv <<- inverse  # Save the inverse
+        getinverse <- function() inv  # Show me the saved inverse
+        list(set = set, 
+             get = get, 
+             setinverse = setinverse, 
+             getinverse = getinverse)  # Put all tools in a box
+}
 
-## Write a short comment describing this function
 
-makeCacheMatrix <- function(x = matrix()) {
+# Looks at the saved inverse in the magic box.
+# If it’s there (not NULL), says “Hey, I found it!” and gives it to you.
+# If it’s not there, gets the matrix, calculates the inverse using a math trick (solve), saves it, and hands it over.
 
+cacheSolve <- function(x, ...) {  # x is the magic box from makeCacheMatrix
+        inv <- x$getinverse()  # Peek at the saved inverse
+        if(!is.null(inv)) {    # If there’s something saved
+                message("Getting cached data!")  # Say we found it
+                return(inv)        # Give the saved inverse
+        }
+        data <- x$get()        # Get the matrix since we need to calculate
+        inv <- solve(data, ...) # Use a math trick to find the inverse
+        x$setinverse(inv)      # Save the inverse in the box
+        inv                    # Give the inverse
 }
 
+# Make the magic box with a matrix
+my_matrix <- makeCacheMatrix(matrix(c(1, 2, 3, 4), 2, 2))
 
-## Write a short comment describing this function
+# First time - calculates inverse
+cacheSolve(my_matrix)
+# Output might be: [-2, 1; 1.5, -0.5]
 
-cacheSolve <- function(x, ...) {
-        ## Return a matrix that is the inverse of 'x'
-}
+# Second time - uses cached version
+cacheSolve(my_matrix)
+# Output: "Getting cached data!" then [-2, 1; 1.5, -0.5]