@Override
    protected void map(IntWritable row, VectorWritable vectorWritable, Context ctx)
        throws IOException, InterruptedException {

      Vector rowVector = similarity.normalize(vectorWritable.get());

      int numNonZeroEntries = 0;
      double maxValue = Double.MIN_VALUE;

      Iterator<Vector.Element> nonZeroElements = rowVector.iterateNonZero();
      while (nonZeroElements.hasNext()) {
        Vector.Element element = nonZeroElements.next();
        RandomAccessSparseVector partialColumnVector =
            new RandomAccessSparseVector(Integer.MAX_VALUE);
        partialColumnVector.setQuick(row.get(), element.get());
        ctx.write(new IntWritable(element.index()), new VectorWritable(partialColumnVector));

        numNonZeroEntries++;
        if (maxValue < element.get()) {
          maxValue = element.get();
        }
      }

      if (threshold != NO_THRESHOLD) {
        nonZeroEntries.setQuick(row.get(), numNonZeroEntries);
        maxValues.setQuick(row.get(), maxValue);
      }
      norms.setQuick(row.get(), similarity.norm(rowVector));

      ctx.getCounter(Counters.ROWS).increment(1);
    }