@Override
protected void map(IntWritable userOrItemID, VectorWritable ratingsWritable, Context ctx)
throws IOException, InterruptedException {
Vector ratings = new SequentialAccessSparseVector(ratingsWritable.get());
List<Vector> featureVectors = Lists.newArrayList();
Iterator<Vector.Element> interactions = ratings.iterateNonZero();
while (interactions.hasNext()) {
int index = interactions.next().index();
featureVectors.add(UorM.get(index));
}