Do assignment -- added tests

Author: abhishekmukherg

cachematrix.R

@@ -1,15 +1,44 @@
 ## Put comments here that give an overall description of what your
 ## functions do
 
-## Write a short comment describing this function
-
+# Returns a container that can hold a matrix, and some cached data computed
+# from the matrix
 makeCacheMatrix <- function(x = matrix()) {
-
+  cached.transposed <- NULL
+  
+  # Update matrices
+  set <- function(y) {
+    x <<- y
+    cached.transposed <<- NULL
+  }
+  get <- function() x
+  
+  # Transposed
+  set.cached.transposed <- function(transposed) {
+    cached.transposed <<- transposed
+  }
+  get.cached.transposed <- function() cached.transposed
+  
+  list(set = set,
+       get = get,
+       set.cached.transposed = set.cached.transposed,
+       get.cached.transposed = get.cached.transposed)
+  
 }
 
 
-## Write a short comment describing this function
-
+## Returns a transposed version of the matrix contained in x
+#
+# This function returns a transposed version of the matrix that is
+# stored in x, and will cache it for subsequent calls
 cacheSolve <- function(x, ...) {
-        ## Return a matrix that is the inverse of 'x'
-}
+  transposed <- x$get.cached.transposed()
+  if (!is.null(transposed)) {
+    message("returning cached transposed matrix")
+    return(transposed)
+  }
+  
+  transposed <- t(x$get(), ...)
+  x$set.cached.transposed(transposed)
+  transposed
+}

tests.R

@@ -0,0 +1,29 @@
+source("cachematrix.R")
+
+assert.cached <- function(m, v) stopifnot(identical(m$get.cached.transposed(), v))
+assert.uncached <- function(m) assert.cached(m, NULL)
+
+# test with null matrix
+m <- makeCacheMatrix(x = matrix())
+
+stopifnot(identical(m$get(), matrix()))
+assert.uncached(m)
+
+stopifnot(identical(cacheSolve(m), matrix()))
+assert.cached(m, matrix())
+stopifnot(identical(m$get(), matrix()))
+
+# Test with actual matrix
+mat <- matrix(c(1, 2, 3, 4), 2, 2)
+m <- makeCacheMatrix(mat)
+stopifnot(identical(m$get(), mat))
+assert.uncached(m)
+stopifnot(identical(cacheSolve(m), t(mat)))
+stopifnot(identical(m$get(), mat))
+assert.cached(m, t(mat))
+
+# Ensure calling set() resets the cache
+mat <- matrix(c(1, 2, 3, 4), 4, 1)
+m$set(mat)
+stopifnot(identical(m$get(), mat))
+assert.uncached(m)