Convert single h5 record to an example dict.

def to_example_dict(encoder, inputs, mask, outputs):
  """Convert single h5 record to an example dict."""
  # Inputs
  bases = []
  input_ids = []
  last_idx = -1
  for row in np.argwhere(inputs):
    idx, base_id = row
    idx, base_id = int(idx), int(base_id)
    assert idx > last_idx  # if not, means 2 True values in 1 row
    # Some rows are all False. Those rows are mapped to UNK_ID.
    while idx != last_idx + 1:
      bases.append(encoder.UNK)
      last_idx += 1
    bases.append(encoder.BASES[base_id])
    last_idx = idx
  assert len(inputs) == len(bases)

  input_ids = encoder.encode(bases)
  input_ids.append(text_encoder.EOS_ID)

  # Targets: mask and output
  targets_mask = [float(v) for v in mask]
  # The output is (n, m); store targets_shape so that it can be reshaped
  # properly on the other end.
  targets = [float(v) for v in outputs.flatten()]
  targets_shape = [int(dim) for dim in outputs.shape]
  assert mask.shape[0] == outputs.shape[0]

  example_keys = ["inputs", "targets_mask", "targets", "targets_shape"]
  ex_dict = dict(
      zip(example_keys, [input_ids, targets_mask, targets, targets_shape]))
  return ex_dict