class_docstr: Desc: Data preprocessing,
        Here, e.g.    15 days for training,
                      3 days for validation,
                      and 6 days for testing
code: def __read_data__(self):
      df_raw = pd.read_csv(os.path.join(self.data_path, self.filename))
      df_data, raw_df_data = self.data_preprocess(df_raw)
      self.df_data = df_data
      self.raw_df_data = raw_df_data
  
      data_x, graph = self.build_graph_data(df_data)
      log.info(f"data_shape: {data_x.shape}")
      log.info(f"graph: {graph}")
      self.data_x = data_x
      self.graph = graph
  
imports: import os
  import time
  import datetime
  import numpy
  import pandas
  import paddle
  from paddle.io import Dataset
  import pgl
  from pgl.utils.logger import log
label_desc: Use image node_id 2 for calling the PGL4WPFDataset obj's underlying member method code with example usage: obj.__read_data__() without return types