code: @Override
      public Object map(Object input) {
          List<Long> list = (List<Long>) input;
          switch (mathOp) {
              case Add:
                  long sum = 0;
                  for (Long w : list)
                      sum += w;
                  return new LongWritable(sum);
              case Subtract:
                  return list.get(0) - list.get(1);
              case Multiply:
                  long product = 1;
                  for (Long w : list)
                      product *= w;
                  return product;
              case Divide:
                  return list.get(0) / list.get(1);
              case Modulus:
                  return list.get(0) % list.get(1);
              case ReverseSubtract:
              case ReverseDivide:
              case ScalarMin:
              case ScalarMax:
              default:
                  throw new RuntimeException("Invalid mathOp: " + mathOp); //Should never happen
          }
      }
docs: Transform an object
  in to another object
  
  @param input the record to transform
  @return the transformed writable