class_docstr: Concatenate fields together using ``np.concatenate``.
  
  Fields with value ``None`` are ignored.
  
  Parameters
  ----------
  output_field
      Field name to use for the output
  input_fields
      Fields to stack together
  drop_inputs
      If set to true the input fields will be dropped.
class_docstr_tok: ["Concatenate","fields","together","using","``","np.concatenate","``",".","Fields","with","value","``","None","``","are","ignored",".","Parameters","--","--","--","--","--","output_field","Field","name","to","use","for","the","output","input_fields","Fields","to","stack","together","drop_inputs","If","set","to","true","the","input","fields","will","be","dropped","."]
code: def __init__(
      self,
      output_field: str,
      input_fields: List[str],
      drop_inputs: bool = True,
  ) -> None:
      self.output_field = output_field
      self.input_fields = input_fields
      self.cols_to_drop = (
          []
          if not drop_inputs
          else [
              fname
              for fname in self.input_fields
              if fname != output_field
          ]
      )
  
imports: from typing import Callable, Iterator, List, Optional, Tuple, Type
  import numpy
  from toolz import valmap
  from gluonts.core.component import validated, tensor_to_numpy
  from gluonts.dataset.common import DataEntry
  from gluonts.exceptions import assert_data_error
  from ._base import FlatMapTransformation, MapTransformation, SimpleTransformation
label_desc: Use image node_id 1 to create a new ConcatFeatures object from inherited base classes: SimpleTransformation with example: obj = ConcatFeatures(output_field, input_fields, drop_inputs)