From fabf1749995103841e6a3975892572f376ee48d0 Mon Sep 17 00:00:00 2001 From: Martin Jaggi Date: Sat, 8 Feb 2014 11:39:13 -0800 Subject: Merge pull request #552 from martinjaggi/master. Closes #552. tex formulas in the documentation using mathjax. and spliting the MLlib documentation by techniques see jira https://spark-project.atlassian.net/browse/MLLIB-19 and https://github.com/shivaram/spark/compare/mathjax Author: Martin Jaggi == Merge branch commits == commit 0364bfabbfc347f917216057a20c39b631842481 Author: Martin Jaggi Date: Fri Feb 7 03:19:38 2014 +0100 minor polishing, as suggested by @pwendell commit dcd2142c164b2f602bf472bb152ad55bae82d31a Author: Martin Jaggi Date: Thu Feb 6 18:04:26 2014 +0100 enabling inline latex formulas with $.$ same mathjax configuration as used in math.stackexchange.com sample usage in the linear algebra (SVD) documentation commit bbafafd2b497a5acaa03a140bb9de1fbb7d67ffa Author: Martin Jaggi Date: Thu Feb 6 17:31:29 2014 +0100 split MLlib documentation by techniques and linked from the main mllib-guide.md site commit d1c5212b93c67436543c2d8ddbbf610fdf0a26eb Author: Martin Jaggi Date: Thu Feb 6 16:59:43 2014 +0100 enable mathjax formula in the .md documentation files code by @shivaram commit d73948db0d9bc36296054e79fec5b1a657b4eab4 Author: Martin Jaggi Date: Thu Feb 6 16:57:23 2014 +0100 minor update on how to compile the documentation --- docs/mllib-collaborative-filtering.md | 130 ++++++++++++++++++++++++++++++++++ 1 file changed, 130 insertions(+) create mode 100644 docs/mllib-collaborative-filtering.md (limited to 'docs/mllib-collaborative-filtering.md') diff --git a/docs/mllib-collaborative-filtering.md b/docs/mllib-collaborative-filtering.md new file mode 100644 index 0000000000..aa22f67b30 --- /dev/null +++ b/docs/mllib-collaborative-filtering.md @@ -0,0 +1,130 @@ +--- +layout: global +title: MLlib - Collaborative Filtering +--- + +* Table of contents +{:toc} + +# 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-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 +(ALS)](http://www2.research.att.com/~volinsky/papers/ieeecomputer.pdf) +algorithm to learn these latent factors. The implementation in MLlib has the +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. +* *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://www2.research.att.com/~yifanhu/PUB/cf.pdf). +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: + +* [ALS](api/mllib/index.html#org.apache.spark.mllib.recommendation.ALS) + + +# Usage in Scala + +Following code snippets can be executed in `spark-shell`. + +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 +model by measuring the Mean Squared Error of rating prediction. + +{% highlight scala %} +import org.apache.spark.mllib.recommendation.ALS +import org.apache.spark.mllib.recommendation.Rating + +// Load and parse the data +val data = sc.textFile("mllib/data/als/test.data") +val ratings = data.map(_.split(',') match { + case Array(user, item, rate) => Rating(user.toInt, item.toInt, rate.toDouble) +}) + +// Build the recommendation model using ALS +val numIterations = 20 +val model = ALS.train(ratings, 1, 20, 0.01) + +// Evaluate the model on rating data +val usersProducts = ratings.map{ case Rating(user, product, rate) => (user, product)} +val predictions = model.predict(usersProducts).map{ + case Rating(user, product, rate) => ((user, product), rate) +} +val ratesAndPreds = ratings.map{ + case Rating(user, product, rate) => ((user, product), rate) +}.join(predictions) +val MSE = ratesAndPreds.map{ + case ((user, product), (r1, r2)) => math.pow((r1- r2), 2) +}.reduce(_ + _)/ratesAndPreds.count +println("Mean Squared Error = " + MSE) +{% endhighlight %} + +If the rating matrix is derived from other source of information (i.e., it is inferred from +other signals), you can use the trainImplicit method to get better results. + +{% highlight scala %} +val model = ALS.trainImplicit(ratings, 1, 20, 0.01) +{% endhighlight %} + +# Usage in Java + +All of MLlib's methods use Java-friendly types, so you can import and call them there the same +way you do in Scala. The only caveat is that the methods take Scala RDD objects, while the +Spark Java API uses a separate `JavaRDD` class. You can convert a Java RDD to a Scala one by +calling `.rdd()` on your `JavaRDD` object. + +# Usage in Python +Following examples can be tested in the PySpark shell. + +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 by measuring the Mean Squared Error of rating prediction. + +{% highlight python %} +from pyspark.mllib.recommendation import ALS +from numpy import array + +# Load and parse the data +data = sc.textFile("mllib/data/als/test.data") +ratings = data.map(lambda line: array([float(x) for x in line.split(',')])) + +# Build the recommendation model using Alternating Least Squares +model = ALS.train(ratings, 1, 20) + +# Evaluate the model on training data +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 +signals), you can use the trainImplicit method to get better results. + +{% highlight python %} +# Build the recommendation model using Alternating Least Squares based on implicit ratings +model = ALS.trainImplicit(ratings, 1, 20) +{% endhighlight %} -- cgit v1.2.3