tfds.features.Sequence

Composite FeatureConnector for a dict where each value is a list.

Sequence correspond to sequence of tfds.features.FeatureConnector. At generation time, a list for each of the sequence element is given. The output of tf.data.Dataset will batch all the elements of the sequence together.

If the length of the sequence is static and known in advance, it should be specified in the constructor using the length param.

Note that Sequence does not support features which are of type tf.io.FixedLenSequenceFeature.

Example:

At construction time:

tfds.features.Sequence(tfds.features.Image(), length=NB_FRAME)

or:

tfds.features.Sequence({
    'frame': tfds.features.Image(shape=(64, 64, 3))
    'action': tfds.features.ClassLabel(['up', 'down', 'left', 'right'])
}, length=NB_FRAME)

During data generation:

yield {
    'frame': np.ones(shape=(NB_FRAME, 64, 64, 3)),
    'action': ['left', 'left', 'up', ...],
}

Tensor returned by .as_dataset():

{
    'frame': tf.Tensor(shape=(NB_FRAME, 64, 64, 3), dtype=tf.uint8),
    'action': tf.Tensor(shape=(NB_FRAME,), dtype=tf.int64),
}

At generation time, you can specify a list of features dict, a dict of list values or a stacked numpy array. The lists will automatically be distributed into their corresponding FeatureConnector.

feature dict, the features to wrap
length int, length of the sequence if static and known in advance
**kwargs dict, constructor kwargs of tfds.features.FeaturesDict

dtype Return the dtype (or dict of dtype) of this FeatureConnector.
feature The inner feature.
shape Return the shape (or dict of shape) of this FeatureConnector.

Methods

decode_batch_example

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Decode multiple features batched in a single tf.Tensor.

This function is used to decode features wrapped in tfds.features.Sequence(). By default, this function apply decode_example on each individual elements using tf.map_fn. However, for optimization, features can overwrite this method to apply a custom batch decoding.

Args
tfexample_data Same tf.Tensor inputs as decode_example, but with and additional first dimension for the sequence length.

Returns
tensor_data Tensor or dictionary of tensor, output of the tf.data.Dataset object

decode_example

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Decode the serialize examples.

Args
serialized_example Nested dict of tf.Tensor
decoders Nested dict of Decoder objects which allow to customize the decoding. The structure should match the feature structure, but only customized feature keys need to be present. See the guide for more info.

Returns
example Nested dict containing the decoded nested examples.

decode_ragged_example

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Decode nested features from a tf.RaggedTensor.

This function is used to decode features wrapped in nested tfds.features.Sequence(). By default, this function apply decode_batch_example on the flat values of the ragged tensor. For optimization, features can overwrite this method to apply a custom batch decoding.

Args
tfexample_data tf.RaggedTensor inputs containing the nested encoded examples.

Returns
tensor_data The decoded tf.RaggedTensor or dictionary of tensor, output of the tf.data.Dataset object

encode_example

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Encode the feature dict into tf-example compatible input.

The input example_data can be anything that the user passed at data generation. For example:

For features:

features={
    'image': tfds.features.Image(),
    'custom_feature': tfds.features.CustomFeature(),
}

At data generation (in _generate_examples), if the user yields:

yield {
    'image': 'path/to/img.png',
    'custom_feature': [123, 'str', lambda x: x+1]
}

Then:

Args
example_data Value or dictionary of values to convert into tf-example compatible data.

Returns
tfexample_data Data or dictionary of data to write as tf-example. Data can be a list or numpy array. Note that numpy arrays are flattened so it's the feature connector responsibility to reshape them in decode_example(). Note that tf.train.Example only supports int64, float32 and string so the data returned here should be integer, float or string. User type can be restored in decode_example().

get_serialized_info

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See base class for details.

get_tensor_info

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See base class for details.

load_metadata

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See base class for details.

save_metadata

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See base class for details.

__getitem__

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Convenience method to access the underlying features.