tf.nest.flatten  |  TensorFlow v2.16.1 (original) (raw)

tf.nest.flatten

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Returns a flat list from a given structure.

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Compat aliases for migration

SeeMigration guide for more details.

tf.compat.v1.nest.flatten

tf.nest.flatten(
    structure, expand_composites=False
)

Used in the notebooks

Refer to tf.nestfor the definition of a structure.

If the structure is an atom, then returns a single-item list: [structure].

This is the inverse of the nest.pack_sequence_as method that takes in a flattened list and re-packs it into the nested structure.

In the case of dict instances, the sequence consists of the values, sorted by key to ensure deterministic behavior. This is true also for OrderedDict instances: their sequence order is ignored, the sorting order of keys is used instead. The same convention is followed in nest.pack_sequence_as. This correctly repacks dicts and OrderedDicts after they have been flattened, and also allows flattening an OrderedDict and then repacking it back using a corresponding plain dict, or vice-versa. Dictionaries with non-sortable keys cannot be flattened.

Users must not modify any collections used in nest while this function is running.

Examples:

1. Python dict (ordered by key):
   dict = { "key3": "value3", "key1": "value1", "key2": "value2" }
tf.nest.flatten(dict)
['value1', 'value2', 'value3']
   
2. For a nested python tuple:
   tuple = ((1.0, 2.0), (3.0, 4.0, 5.0), 6.0)
tf.nest.flatten(tuple)
[1.0, 2.0, 3.0, 4.0, 5.0, 6.0]

3. For a nested dictionary of dictionaries:
dict = { "key3": {"c": (1.0, 2.0), "a": (3.0)},
"key1": {"m": "val1", "g": "val2"} }
tf.nest.flatten(dict)
['val2', 'val1', 3.0, 1.0, 2.0]
4. Numpy array (will not flatten):
array = np.array([[1, 2], [3, 4]])
tf.nest.flatten(array)
[array([[1, 2],
[3, 4]])]
5. tf.Tensor (will not flatten):
tensor = tf.constant([[1., 2., 3.], [4., 5., 6.], [7., 8., 9.]])
tf.nest.flatten(tensor)
[<tf.Tensor: shape=(3, 3), dtype=float32, numpy=
array([[1., 2., 3.],
[4., 5., 6.],
[7., 8., 9.]], dtype=float32)>]
6. tf.RaggedTensor: This is a composite tensor thats representation consists of a flattened list of 'values' and a list of 'row_splits' which indicate how to chop up the flattened list into different rows. For more details ontf.RaggedTensor, please visit https://www.tensorflow.org/api\_docs/python/tf/RaggedTensor.

with expand_composites=False, we just return the RaggedTensor as is.

tensor = tf.ragged.constant([[3, 1, 4, 1], [], [5, 9, 2]]) tf.nest.flatten(tensor, expand_composites=False) [<tf.RaggedTensor [[3, 1, 4, 1], [], [5, 9, 2]]>]

with expand_composites=True, we return the component Tensors that make up the RaggedTensor representation (the values and row_splits tensors)

tensor = tf.ragged.constant([[3, 1, 4, 1], [], [5, 9, 2]]) tf.nest.flatten(tensor, expand_composites=True) [<tf.Tensor: shape=(7,), dtype=int32, numpy=array([3, 1, 4, 1, 5, 9, 2], dtype=int32)>, <tf.Tensor: shape=(4,), dtype=int64, numpy=array([0, 4, 4, 7])>]