@Override
protected void reduce(VarLongWritable itemID, Iterable<VarLongWritable> values, Context ctx)
throws IOException, InterruptedException {
int itemIDIndex = TasteHadoopUtils.idToIndex(itemID.get());
Vector vector = new RandomAccessSparseVector(Integer.MAX_VALUE, 1);
/* artificial NaN summand to exclude this item from the recommendations for all users specified in userIDs */
vector.set(itemIDIndex, Double.NaN);
// 这是过滤的trick
// 从这里可以反推出来,AggregateAndRecommendReducer里面过滤了评分过的 user,item这种pair
List<Long> userIDs = Lists.newArrayList();
List<Float> prefValues = Lists.newArrayList();
for (VarLongWritable userID : values) {
userIDs.add(userID.get());
prefValues.add(1.0f);
}
itemIDIndexWritable.set(itemIDIndex);
vectorAndPrefs.set(vector, userIDs, prefValues);
ctx.write(itemIDIndexWritable, vectorAndPrefs);
}
