Added proper evaluation example for collaborative filtering and fixed typo

1 files changed, 8 insertions, 4 deletions

diff --git a/docs/mllib-guide.md b/docs/mllib-guide.md
index 3fd3c91e2a..5f3b676126 100644
--- a/docs/mllib-guide.md
+++ b/docs/mllib-guide.md
@@ -3,7 +3,7 @@ layout: global
 title: Machine Learning Library (MLlib)
 ---
 
-* Table of contests
+* Table of contents
 {:toc}
 
 MLlib is a Spark implementation of some common machine learning (ML)
@@ -403,8 +403,8 @@ Errors.
 
 ## Collaborative Filtering
 In the following example we load rating data. Each row consists of a user, a product and a rating.
-We use the default ALS.train() method which assumes ratings are explicit. We evaluate the recommendation
-on one example.
+We use the default ALS.train() method which assumes ratings are explicit. We evaluate the
+recommendation by measuring the Mean Squared Error of rating prediction.
 
 {% highlight python %}
 from pyspark.mllib.recommendation import ALS
@@ -418,7 +418,11 @@ ratings = data.map(lambda line: array([float(x) for x in line.split(',')]))
 model = ALS.train(sc, ratings, 1, 20)
 
 # Evaluate the model on training data
-print("predicted rating of user {0} for item {1} is {2:.6}".format(1, 2, model.predict(1, 2)))
+testdata = ratings.map(lambda p: (int(p[0]), int(p[1])))
+predictions = model.predictAll(testdata).map(lambda r: ((r[0], r[1]), r[2]))
+ratesAndPreds = ratings.map(lambda r: ((r[0], r[1]), r[2])).join(predictions)
+MSE = ratesAndPreds.map(lambda r: (r[1][0] - r[1][1])**2).reduce(lambda x, y: x + y)/ratesAndPreds.count()
+print("Mean Squared Error = " + str(MSE))
 {% endhighlight %}
 
 If the rating matrix is derived from other source of information (i.e., it is inferred from other