mahout推荐引擎使用hadoop（三） 协同矩阵与用户向量相乘

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?下边也是同样分析一下这个三个MapReduce的细节：

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1、Mapper： SimilarityMatrixRowWrapperMapper 类，将协同矩阵的一行拿出来，通过包装，封装成VectorOrPrefWritable类，与那边的UserVectorSplitterMapper 的输出类型一致

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第四步，协同矩阵和用户向量相乘，得到推荐结果
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public final class PartialMultiplyMapper extends    Mapper<VarIntWritable,VectorAndPrefsWritable,VarLongWritable,PrefAndSimilarityColumnWritable> {  @Override  protected void map(VarIntWritable key,                     VectorAndPrefsWritable vectorAndPrefsWritable,                     Context context) throws IOException, InterruptedException {    Vector similarityMatrixColumn = vectorAndPrefsWritable.getVector();    List<Long> userIDs = vectorAndPrefsWritable.getUserIDs();    List<Float> prefValues = vectorAndPrefsWritable.getValues();    VarLongWritable userIDWritable = new VarLongWritable();    PrefAndSimilarityColumnWritable prefAndSimilarityColumn = new PrefAndSimilarityColumnWritable();    for (int i = 0; i < userIDs.size(); i++) {      long userID = userIDs.get(i);      float prefValue = prefValues.get(i);      if (!Float.isNaN(prefValue)) {        prefAndSimilarityColumn.set(prefValue, similarityMatrixColumn);        userIDWritable.set(userID);        context.write(userIDWritable, prefAndSimilarityColumn);      }    }  }}
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