code: private VertexProgram initStatisticsVertexProgram(GraqlCompute query, Set<LabelId> targetTypes, AttributeType.DataType<?> targetDataType) {
          if (query.method().equals(MEDIAN)) return new MedianVertexProgram(targetTypes, targetDataType);
          else return new DegreeStatisticsVertexProgram(targetTypes);
      }
docs: Helper method to intialise the vertex program for compute statistics queries
  
  @param query          representing the compute query
  @param targetTypes    representing the attribute types in which the statistics computation is targeted for
  @param targetDataType representing the data type of the target attribute types
  @return an object which is a subclass of VertexProgram