code: def group_by_reducer(key_func, reducer):
      """A transformation that groups elements and performs a reduction.
  
      This transformation maps element of a dataset to a key using `key_func` and
      groups the elements by key. The `reducer` is used to process each group; its
      `init_func` is used to initialize state for each group when it is created, the
      `reduce_func` is used to update the state every time an element is mapped to
      the matching group, and the `finalize_func` is used to map the final state to
      an output value.
  
      Args:
        key_func: A function mapping a nested structure of tensors
          (having shapes and types defined by `self.output_shapes` and
          `self.output_types`) to a scalar `tf.int64` tensor.
        reducer: An instance of `Reducer`, which captures the reduction logic using
          the `init_func`, `reduce_func`, and `finalize_func` functions.
  
      Returns:
        A `Dataset` transformation function, which can be passed to
        `tf.data.Dataset.apply`.
      """
  
      def _apply_fn(dataset):
          """Function from `Dataset` to `Dataset` that applies the transformation."""
          return _GroupByReducerDataset(dataset, key_func, reducer)
  
      return _apply_fn
  
imports: from tensorflow.python.data.ops import dataset_ops
  from tensorflow.python.data.ops import structured_function
  from tensorflow.python.data.util import nest
  from tensorflow.python.data.util import structure
  from tensorflow.python.framework import dtypes
  from tensorflow.python.framework import ops
  from tensorflow.python.framework import tensor_spec
  from tensorflow.python.ops import gen_experimental_dataset_ops
  from tensorflow.python.util import deprecation
  from tensorflow.python.util.tf_export import tf_export
label_desc: Use image node_id 1 for calling a global function with example usage: group_by_reducer(key_func, reducer) and returns: _apply_fn, _GroupByReducerDataset