✨ add to_pyg_data function

    ----------

    node_features : np.ndarray

      Node feature matrix with shape [num_nodes, num_node_features]

    edge_index : np.ndarray

    edge_index : np.ndarray, dtype int

      Graph connectivity in COO format with shape [2, num_edges]

    targets : np.ndarray

      Graph or node targets with arbitrary shape

      raise ValueError('node_features must be np.ndarray.')

    if isinstance(edge_index, np.ndarray) is False:

      raise ValueError('edge_index must be np.ndarray.')

    elif edge_index.dtype != np.int:

      raise ValueError('edge_index.dtype must be np.int')

    elif edge_index.shape[0] != 2:

      raise ValueError('The shape of edge_index is [2, num_edges].')

    if isinstance(targets, np.ndarray) is False:

    if self.node_features is not None:

      self.num_edge_features = self.edge_features.shape[1]

  def to_pyg_data(self):

    """"Convert to Pytorch Geometric data class"""

    try:

      import torch

      from torch_geometric.data import Data

    except ModuleNotFoundError:

      raise ValueError(

          "This class requires Pytorch and PyTorch Geometric to be installed.")

    return Data(

      x=torch.from_numpy(self.node_features),

      edge_index=torch.from_numpy(self.edge_index),

      edge_attr=None if self.edge_features is None \

        else torch.from_numpy(self.edge_features),

      y=torch.from_numpy(self.targets),

    )

class BatchMoleculeGraphData(MoleculeGraphData):

  """Batch MoleculeGraphData class