tf.data.experimental.get_single_element

Returns the single element of the dataset as a nested structure of tensors. (deprecated)

tf.data.experimental.get_single_element(
    dataset
)

The function enables you to use a tf.data.Dataset in a stateless "tensor-in tensor-out" expression, without creating an iterator. This facilitates the ease of data transformation on tensors using the optimized tf.data.Dataset abstraction on top of them.

For example, lets consider a preprocessing_fn which would take as an input the raw features and returns the processed feature along with it's label.

def preprocessing_fn(raw_feature):
  # ... the raw_feature is preprocessed as per the use-case
  return feature

raw_features = ...  # input batch of BATCH_SIZE elements.
dataset = (tf.data.Dataset.from_tensor_slices(raw_features)
           .map(preprocessing_fn, num_parallel_calls=BATCH_SIZE)
           .batch(BATCH_SIZE))

processed_features = tf.data.experimental.get_single_element(dataset)

In the above example, the raw_features tensor of length=BATCH_SIZE was converted to a tf.data.Dataset. Next, each of the raw_feature was mapped using the preprocessing_fn and the processed features were grouped into a single batch. The final dataset contains only one element which is a batch of all the processed features.

Now, instead of creating an iterator for the dataset and retrieving the batch of features, the tf.data.experimental.get_single_element() function is used to skip the iterator creation process and directly output the batch of features.

This can be particularly useful when your tensor transformations are expressed as tf.data.Dataset operations, and you want to use those transformations while serving your model.

Keras


model = ... # A pre-built or custom model

class PreprocessingModel(tf.keras.Model):
  def __init__(self, model):
    super().__init__(self)
    self.model = model

  @tf.function(input_signature=[...])
  def serving_fn(self, data):
    ds = tf.data.Dataset.from_tensor_slices(data)
    ds = ds.map(preprocessing_fn, num_parallel_calls=BATCH_SIZE)
    ds = ds.batch(batch_size=BATCH_SIZE)
    return tf.argmax(
      self.model(tf.data.experimental.get_single_element(ds)),
      axis=-1
    )

preprocessing_model = PreprocessingModel(model)
your_exported_model_dir = ... # save the model to this path.
tf.saved_model.save(preprocessing_model, your_exported_model_dir,
              signatures={'serving_default': preprocessing_model.serving_fn})

dataset A tf.data.Dataset object containing a single element.

A nested structure of tf.Tensor objects, corresponding to the single element of dataset.

TypeError if dataset is not a tf.data.Dataset object.
InvalidArgumentError (at runtime) if dataset does not contain exactly one element.