code: def batch(states, batch_size=None):
      """Combines a collection of state structures into a batch, padding if needed.
  
      Args:
        states: A collection of individual nested state structures.
        batch_size: The desired final batch size. If the nested state structure
            that results from combining the states is smaller than this, it will be
            padded with zeros.
      Returns:
        A single state structure that results from stacking the structures in
        `states`, with padding if needed.
  
      Raises:
        ValueError: If the number of input states is larger than `batch_size`.
      """
      if batch_size and len(states) > batch_size:
          raise ValueError(
              "Combined state is larger than the requested batch size"
          )
  
      def stack_and_pad(*states):
          stacked = np.stack(states)
          if batch_size:
              stacked = np.pad(
                  stacked,
                  [(0, batch_size - stacked.shape[0])]
                  + [(0, 0)] * (len(stacked.shape) - 1),
              )
          return stacked
  
      return tf.nest.map_structure(stack_and_pad, *states)
  
imports: import numpy
  import tensorflow.compat.v1
label_desc: Use image node_id 3 for calling a global function with example usage: batch(states, batch_size) and returns: tf, stacked