@Override
  public int compareTo(Vertex o) {
    // we print the vertex that has more rs before the vertex that has fewer rs.
    if (numReduceOp != o.numReduceOp) {
      return -(numReduceOp - o.numReduceOp);
    } else {
      return this.name.compareTo(o.name);
    }
  }
We check if a vertex has multiple reduce operators.
@throws JSONException
common/src/java/org/apache/hadoop/hive/common/jsonexplain/Vertex.java