class_docstr: Wrapper that concatenates observation fields.
  
  It takes an environment with nested observations and concatenates the fields
  in a single tensor. The original fields should be 1-dimensional.
  Observation fields that are not in name_filter are dropped.
  
  **NOTE**: The fields in the flattened observations will be in sorted order by
  their names, see tree.flatten for more information.
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code: def _convert_observation(self, observation):
      obs = {k: observation[k] for k in self._obs_names}
      return _concat(obs)
  
file_path: acme/acme/wrappers/concatenate_observations.py
imports: from typing import Sequence, Optional
  from acme import types
  from acme.wrappers import base
  import dm_env
  import numpy
  import tree
label_desc: Use image node_id 2 for calling the ConcatObservationWrapper obj's underlying member method code with example usage: obj._convert_observation(observation) and returns: _concat