Taste 是 Apache Mahout 提供的一个协同过滤算法的高效实现，它是一个基于Java实现的可扩展的高效的推荐引擎。扩展性是指使用hadoop进行mapreduce计算，提高运算性能。
最近开始看源码，分析一下，做个笔记。 ItemSimilarityJob类是mahout使用hadoop做推荐引擎的主要实现类，下面开始分析。
run()函数是启动函数：
public final class RecommenderJob extends AbstractJob {
public static final String BOOLEAN_DATA = "booleanData";
private static final int DEFAULT_MAX_SIMILARITIES_PER_ITEM = 100;
private static final int DEFAULT_MAX_PREFS_PER_USER = 1000;
private static final int DEFAULT_MIN_PREFS_PER_USER = 1;
@Override
public int run(String[] args) throws Exception {
//这里原来有大一堆代码，都是用来载入配置项，不用管它
//第一步：准备矩阵，将原始数据转换为一个矩阵，在PreparePreferenceMatrixJob这个类中完成
if (shouldRunNextPhase(parsedArgs, currentPhase)) {
ToolRunner.run(getConf(), new PreparePreferenceMatrixJob(), new String[]{
"--input", getInputPath().toString(),
"--output", prepPath.toString(),
"--maxPrefsPerUser", String.valueOf(maxPrefsPerUserInItemSimilarity),
"--minPrefsPerUser", String.valueOf(minPrefsPerUser),
"--booleanData", String.valueOf(booleanData),
"--tempDir", getTempPath().toString()});
numberOfUsers = HadoopUtil.readInt(new Path(prepPath, PreparePreferenceMatrixJob.NUM_USERS), getConf());
}
//第二步：计算协同矩阵
if (shouldRunNextPhase(parsedArgs, currentPhase)) {
/* special behavior if phase 1 is skipped */
if (numberOfUsers == -1) {
numberOfUsers = (int) HadoopUtil.countRecords(new Path(prepPath, PreparePreferenceMatrixJob.USER_VECTORS),
PathType.LIST, null, getConf());
}
/* Once DistributedRowMatrix uses the hadoop 0.20 API, we should refactor this call to something like
* new DistributedRowMatrix(...).rowSimilarity(...) */
//calculate the co-occurrence matrix
ToolRunner.run(getConf(), new RowSimilarityJob(), new String[]{
"--input", new Path(prepPath, PreparePreferenceMatrixJob.RATING_MATRIX).toString(),
"--output", similarityMatrixPath.toString(),
"--numberOfColumns", String.valueOf(numberOfUsers),
"--similarityClassname", similarityClassname,
"--maxSimilaritiesPerRow", String.valueOf(maxSimilaritiesPerItem),
"--excludeSelfSimilarity", String.valueOf(Boolean.TRUE),
"--threshold", String.valueOf(threshold),
"--tempDir", getTempPath().toString()});
}
//start the multiplication of the co-occurrence matrix by the user vectors
if (shouldRunNextPhase(parsedArgs, currentPhase)) {
Job prePartialMultiply1 = prepareJob(
similarityMatrixPath, prePartialMultiplyPath1, SequenceFileInputFormat.class,
SimilarityMatrixRowWrapperMapper.class, VarIntWritable.class, VectorOrPrefWritable.class,
Reducer.class, VarIntWritable.class, VectorOrPrefWritable.class,
SequenceFileOutputFormat.class);
boolean succeeded = prePartialMultiply1.waitForCompletion(true);
if (!succeeded)
return -1;
//continue the multiplication
Job prePartialMultiply2 = prepareJob(new Path(prepPath, PreparePreferenceMatrixJob.USER_VECTORS),
prePartialMultiplyPath2, SequenceFileInputFormat.class, UserVectorSplitterMapper.class, VarIntWritable.class,
VectorOrPrefWritable.class, Reducer.class, VarIntWritable.class, VectorOrPrefWritable.class,
SequenceFileOutputFormat.class);
if (usersFile != null) {
prePartialMultiply2.getConfiguration().set(UserVectorSplitterMapper.USERS_FILE, usersFile);
}
prePartialMultiply2.getConfiguration().setInt(UserVectorSplitterMapper.MAX_PREFS_PER_USER_CONSIDERED,
maxPrefsPerUser);
succeeded = prePartialMultiply2.waitForCompletion(true);
if (!succeeded)
return -1;
//finish the job
Job partialMultiply = prepareJob(
new Path(prePartialMultiplyPath1 + "," + prePartialMultiplyPath2), partialMultiplyPath,
SequenceFileInputFormat.class, Mapper.class, VarIntWritable.class, VectorOrPrefWritable.class,
ToVectorAndPrefReducer.class, VarIntWritable.class, VectorAndPrefsWritable.class,
SequenceFileOutputFormat.class);
setS3SafeCombinedInputPath(partialMultiply, getTempPath(), prePartialMultiplyPath1, prePartialMultiplyPath2);
succeeded = partialMultiply.waitForCompletion(true);
if (!succeeded)
return -1;
}
if (shouldRunNextPhase(parsedArgs, currentPhase)) {
//filter out any users we don't care about
/* convert the user/item pairs to filter if a filterfile has been specified */
if (filterFile != null) {
Job itemFiltering = prepareJob(new Path(filterFile), explicitFilterPath, TextInputFormat.class,
ItemFilterMapper.class, VarLongWritable.class, VarLongWritable.class,
ItemFilterAsVectorAndPrefsReducer.class, VarIntWritable.class, VectorAndPrefsWritable.class,
SequenceFileOutputFormat.class);
boolean succeeded = itemFiltering.waitForCompletion(true);
if (!succeeded)
return -1;
}
String aggregateAndRecommendInput = partialMultiplyPath.toString();
if (filterFile != null) {
aggregateAndRecommendInput += "," + explicitFilterPath;
}
//extract out the recommendations
Job aggregateAndRecommend = prepareJob(
new Path(aggregateAndRecommendInput), outputPath, SequenceFileInputFormat.class,
PartialMultiplyMapper.class, VarLongWritable.class, PrefAndSimilarityColumnWritable.class,
AggregateAndRecommendReducer.class, VarLongWritable.class, RecommendedItemsWritable.class,
TextOutputFormat.class);
Configuration aggregateAndRecommendConf = aggregateAndRecommend.getConfiguration();
if (itemsFile != null) {
aggregateAndRecommendConf.set(AggregateAndRecommendReducer.ITEMS_FILE, itemsFile);
}
if (filterFile != null) {
setS3SafeCombinedInputPath(aggregateAndRecommend, getTempPath(), partialMultiplyPath, explicitFilterPath);
}
setIOSort(aggregateAndRecommend);
aggregateAndRecommendConf.set(AggregateAndRecommendReducer.ITEMID_INDEX_PATH,
new Path(prepPath, PreparePreferenceMatrixJob.ITEMID_INDEX).toString());
aggregateAndRecommendConf.setInt(AggregateAndRecommendReducer.NUM_RECOMMENDATIONS, numRecommendations);
aggregateAndRecommendConf.setBoolean(BOOLEAN_DATA, booleanData);
boolean succeeded = aggregateAndRecommend.waitForCompletion(true);
if (!succeeded)
return -1;
}
return 0;
}
