1、今天试验SlopeOne推荐算法，结果没有提示。心想是不是少了jar包，查查不少。通过网络查询定位此类所在的位置为：org.apache.mahout.cf.taste.impl.recommender.slopeone.包下面，所以去查看jar包，发现没有。查看src包也没有这个类的源码，之后去官网查看，一看，才知道这个算法已被移除了在0.9上。如果想用的话需要0.8.

1 February 2014 - Apache Mahout 0.9 releasedApache Mahout has reached version 0.9. All developers are encouraged to begin using version 0.9. Highlights include:    New and improved Mahout website based on Apache CMS - MAHOUT-1245    Early implementation of a Multi Layer Perceptron (MLP) classifier - MAHOUT-1265    Scala DSL Bindings for Mahout Math Linear Algebra. See this blogpost and MAHOUT-1297    Recommenders as Search. See [https://github.com/pferrel/solr-recommender] and MAHOUT-1288    Support for easy functional Matrix views and derivatives - MAHOUT-1300    JSON output format for ClusterDumper - MAHOUT-1343    Enabled randomised testing for all Mahout modules using Carrot RandomizedRunner - MAHOUT-1345    Online Algorithm for computing accurate Quantiles using 1-dimensional Clustering - See this pdf and MAHOUT-1361    Upgrade to Lucene 4.6.1 - MAHOUT-1364Changes in 0.9 are detailed in the release notes.The following algorithms that were marked deprecated in 0.8 have been removed in 0.9:    Switched LDA implementation from Gibbs Sampling to Collapsed Variational Bayes    Meanshift - removed due to lack of actual usage and support    MinHash - removed due to lack of actual usage and support    Winnow - removed due to lack of actual usage and support    Perceptron - removed due to lack of actual usage and support    Slope One - removed due to lack of actual usage    Distributed Pseudo recommender - removed due to lack of actual usage    TreeClusteringRecommender - removed due to lack of actual usage