class_docstr: Class implementing Imputer operators in MissingIndicator.
code: def forward(self, x):
      if self.is_nan:
          if self.features == "all":
              return torch.isnan(x).float()
          else:
              return torch.isnan(
                  torch.index_select(x, 1, self.column_indices)
              ).float()
      else:
          if self.features == "all":
              return torch.eq(x, self.missing_values).float()
          else:
              return torch.eq(
                  torch.index_select(x, 1, self.column_indices),
                  self.missing_values,
              ).float()
  
file_path: hummingbird/hummingbird/ml/operator_converters/_imputer_implementations.py
imports: import torch
  import numpy
  from ._physical_operator import PhysicalOperator
  from .None import constants
label_desc: Use image node_id 2 for calling the MissingIndicator obj's underlying member method code with example usage: obj.forward(x) and returns: torch, torch, torch, torch