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From s..@apache.org
Subject svn commit: r1575717 - /mahout/site/mahout_cms/trunk/content/users/recommender/userbased-5-minutes.mdtext
Date Sun, 09 Mar 2014 16:06:10 GMT
Author: ssc
Date: Sun Mar  9 16:06:10 2014
New Revision: 1575717

URL: http://svn.apache.org/r1575717
Log:
MAHOUT-1438  quickstart tutorial for building a simple recommender

Added:
    mahout/site/mahout_cms/trunk/content/users/recommender/userbased-5-minutes.mdtext   (with
props)

Added: mahout/site/mahout_cms/trunk/content/users/recommender/userbased-5-minutes.mdtext
URL: http://svn.apache.org/viewvc/mahout/site/mahout_cms/trunk/content/users/recommender/userbased-5-minutes.mdtext?rev=1575717&view=auto
==============================================================================
--- mahout/site/mahout_cms/trunk/content/users/recommender/userbased-5-minutes.mdtext (added)
+++ mahout/site/mahout_cms/trunk/content/users/recommender/userbased-5-minutes.mdtext Sun
Mar  9 16:06:10 2014
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+Title:
+Notice:    Licensed to the Apache Software Foundation (ASF) under one
+           or more contributor license agreements.  See the NOTICE file
+           distributed with this work for additional information
+           regarding copyright ownership.  The ASF licenses this file
+           to you under the Apache License, Version 2.0 (the
+           "License"); you may not use this file except in compliance
+           with the License.  You may obtain a copy of the License at
+           .
+             http://www.apache.org/licenses/LICENSE-2.0
+           .
+           Unless required by applicable law or agreed to in writing,
+           software distributed under the License is distributed on an
+           "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+           KIND, either express or implied.  See the License for the
+           specific language governing permissions and limitations
+           under the License.
+
+# Creating a User-Based Recommender in 5 minutes
+
+##Prerequisites
+
+Create a java project in your favorite IDE and make sure mahout is on the classpath. The
easiest way to accomplish this is by importing it via maven as described on the [Quickstart](/users/basics/quickstart.html)
page.
+
+
+## Dataset
+
+Mahout's recommenders expect interactions between users and items as input. The easiest way
to supply such data to Mahout is in the form of a textfile, where every line has the format
*userID,itemID,value*. Here *userID* and *itemID* refer to a particular user and a particular
item, and *value* denotes the strength of the interaction (e.g. the rating given to a movie).
+
+In this example, we'll use some made up data for simplicity. Create a file called "dataset.csv"
and copy the following example interactions into the file. 
+
+<pre>
+1,10,1.0
+1,11,2.0
+1,12,5.0
+1,13,5.0
+1,14,5.0
+1,15,4.0
+1,16,5.0
+1,17,1.0
+1,18,5.0
+2,10,1.0
+2,11,2.0
+2,15,5.0
+2,16,4.5
+2,17,1.0
+2,18,5.0
+3,11,2.5
+3,12,4.5
+3,13,4.0
+3,14,3.0
+3,15,3.5
+3,16,4.5
+3,17,4.0
+3,18,5.0
+4,10,5.0
+4,11,5.0
+4,12,5.0
+4,13,0.0
+4,14,2.0
+4,15,3.0
+4,16,1.0
+4,17,4.0
+4,18,1.0
+</pre>
+
+## Creating a user-based recommender
+
+Create a class called *SampleRecommender* with a main method.
+
+The first thing we have to do is load the data from the file. Mahout's recommenders use an
interface called *DataModel* to handle interaction data. You can load our made up interactions
like this:
+
+<pre>
+DataModel model = new FileDataModel(new File("/path/to/dataset.csv"));
+</pre>
+
+In this example, we want to create a user-based recommender. The idea behind this approach
is that when we want to compute recommendations for a particular users, we look for other
users with a similar taste and pick the recommendations from their items. For finding similar
users, we have to compare their interactions. There are several methods for doing this. One
popular method is to compute the [correlation coefficient](https://en.wikipedia.org/wiki/Pearson_product-moment_correlation_coefficient)
between their interactions. In Mahout, you use this method as follows:
+
+<pre>
+UserSimilarity similarity = new PearsonCorrelationSimilarity(model);
+</pre>
+
+The next thing we have to do is to define which similar users we want to leverage for the
recommender. For the sake of simplicity, we'll use all that have a similarity greater than
*0.1*. This is implemented via a *ThresholdUserNeighborhood*:
+
+<pre>UserNeighborhood neighborhood = new ThresholdUserNeighborhood(0.1, similarity,
model);</pre>
+
+Now we have all the pieces to create our recommender:
+
+<pre>
+UserBasedRecommender recommender = new GenericUserBasedRecommender(model, neighborhood, similarity);
+</pre>
+        
+We can easily ask the recommender for recommendations now. If we wanted to get three items
recommended for the user with *userID* 2, we would do it like this:
+	
+
+<pre>
+List<RecommendedItem> recommendations = recommender.recommend(2, 3);
+for (RecommendedItem recommendation : recommendations) {
+  System.out.println(recommendation);
+}
+</pre>
+
+
+Congratulations, you have built your first recommender!
+
+
+## Evaluation
+
+You might ask yourself, how to make sure that your recommender returns good results. Unfortunately,
the only way to be really sure about the quality is by doing an A/B test with real users in
a live system.
+
+We can however try to get a feel of the quality, by statistical offline evaluation. Just
keep in mind that this does not replace a test with real users!
+
+One way to check whether the recommender returns good results is by doing a **hold-out**
test. We partition our dataset into two sets: a trainingset consisting of 90% of the data
and a testset consisting of 10%. Then we train our recommender using the training set and
look how well it predicts the unknown interactions in the testset.
+
+To test our recommender, we create a class called *EvaluateRecommender* with a main method
and add an inner class called *MyRecommenderBuilder* that implements the *RecommenderBuilder*
interface. We implement the *buildRecommender* method and make it setup our user-based recommender:
+
+<pre>
+UserSimilarity similarity = new PearsonCorrelationSimilarity(dataModel);
+UserNeighborhood neighborhood = new ThresholdUserNeighborhood(0.1, similarity, dataModel);
+return new GenericUserBasedRecommender(dataModel, neighborhood, similarity);
+</pre>
+
+Now we have to create the code for the test. We'll check how much the recommender misses
the real interaction strength on average. We employ an *AverageAbsoluteDifferenceRecommenderEvaluator*
for this. The following code shows how to put the pieces together and run a hold-out test:

+
+<pre>
+DataModel model = new FileDataModel(new File("/path/to/dataset.csv"));
+RecommenderEvaluator evaluator = new AverageAbsoluteDifferenceRecommenderEvaluator();
+RecommenderBuilder builder = new MyRecommenderBuilder();
+double result = evaluator.evaluate(builder, null, model, 0.9, 1.0);
+System.out.println(result);
+</pre>
+
+Note: if you run this test multiple times, you will get different results, because the splitting
into trainingset and testset is done randomly. 
+
+
+
+
+
+
+
+
+
+
+

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