code: def stack_forest(forest: PyTree) -> PyTree:
      """Transposes a list of dicts to dict of lists.
  
      For example,
      given
      [{'a':1,'b':2}, {'a':3,'b':4}],
      the output is:
      {'a': ([1, 3]), 'b': ([2, 4])}
  
      Args:
        forest: a list of dicts
  
      Returns:
        a dict of lists.
      """
      if not forest:
          return {}
  
      stack_args = lambda *args: np.stack(args)
      return jax.tree_util.tree_map(stack_args, *forest)
  
imports: import collections.abc
  import copy
  import functools
  import os
  import re
  import time
  from typing import Any, Callable, Dict, Mapping, Optional, Sequence, Tuple, Union
  from absl import logging
  from clu import metric_writers
  import flax
  from flax import jax_utils
  from flax import struct
  import flax.linen
  from flax.training import checkpoints
  import jax
  import jax.numpy
  import ml_collections
  import numpy
  import optax
  from scenic.common_lib import debug_utils
  from scenic.dataset_lib import dataset_utils
  from scenic.dataset_lib import datasets
  from scenic.train_lib import optimizers
  from tensorflow.io import gfile
label_desc: Use image node_id 13 for calling a global function with example usage: stack_forest(forest) and returns: jax, dict