Merge branch 'master' of github.com:apache/incubator-spark into scala-2.10

2 files changed, 21 insertions, 5 deletions

diff --git a/docs/mllib-guide.md b/docs/mllib-guide.md
index f991d86c8d..c1ff9c417c 100644
--- a/docs/mllib-guide.md
+++ b/docs/mllib-guide.md
@@ -144,10 +144,9 @@ Available algorithms for clustering:
 
 # Collaborative Filtering 
 
-[Collaborative
-filtering](http://en.wikipedia.org/wiki/Recommender_system#Collaborative_filtering)
+[Collaborative filtering](http://en.wikipedia.org/wiki/Recommender_system#Collaborative_filtering)
 is commonly used for recommender systems.  These techniques aim to fill in the
-missing entries of a user-product association matrix.  MLlib currently supports
+missing entries of a user-item association matrix.  MLlib currently supports
 model-based collaborative filtering, in which users and products are described
 by a small set of latent factors that can be used to predict missing entries.
 In particular, we implement the [alternating least squares
@@ -158,7 +157,24 @@ following parameters:
 * *numBlocks* is the number of blacks used to parallelize computation (set to -1 to auto-configure). 
 * *rank* is the number of latent factors in our model.
 * *iterations* is the number of iterations to run.
-* *lambda* specifies the regularization parameter in ALS. 
+* *lambda* specifies the regularization parameter in ALS.
+* *implicitPrefs* specifies whether to use the *explicit feedback* ALS variant or one adapted for *implicit feedback* data
+* *alpha* is a parameter applicable to the implicit feedback variant of ALS that governs the *baseline* confidence in preference observations
+
+## Explicit vs Implicit Feedback
+
+The standard approach to matrix factorization based collaborative filtering treats 
+the entries in the user-item matrix as *explicit* preferences given by the user to the item.
+
+It is common in many real-world use cases to only have access to *implicit feedback* 
+(e.g. views, clicks, purchases, likes, shares etc.). The approach used in MLlib to deal with 
+such data is taken from 
+[Collaborative Filtering for Implicit Feedback Datasets](http://research.yahoo.com/pub/2433).
+Essentially instead of trying to model the matrix of ratings directly, this approach treats the data as 
+a combination of binary preferences and *confidence values*. The ratings are then related 
+to the level of confidence in observed user preferences, rather than explicit ratings given to items. 
+The model then tries to find latent factors that can be used to predict the expected preference of a user
+for an item. 
 
 Available algorithms for collaborative filtering: 
 
diff --git a/docs/python-programming-guide.md b/docs/python-programming-guide.md
index f67a1cc49c..6c2336ad0c 100644
--- a/docs/python-programming-guide.md
+++ b/docs/python-programming-guide.md
@@ -16,7 +16,7 @@ This guide will show how to use the Spark features described there in Python.
 There are a few key differences between the Python and Scala APIs:
 
 * Python is dynamically typed, so RDDs can hold objects of multiple types.
-* PySpark does not yet support a few API calls, such as `lookup`, `sort`, and non-text input files, though these will be added in future releases.
+* PySpark does not yet support a few API calls, such as `lookup` and non-text input files, though these will be added in future releases.
 
 In PySpark, RDDs support the same methods as their Scala counterparts but take Python functions and return Python collection types.
 Short functions can be passed to RDD methods using Python's [`lambda`](http://www.diveintopython.net/power_of_introspection/lambda_functions.html) syntax: