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Flattens input_tree
up to shallow_tree
.
tf.contrib.framework.nest.flatten_up_to(
shallow_tree, input_tree, check_types=True, expand_composites=False,
check_subtrees_length=True
)
Any further depth in structure in input_tree
is retained as elements in the
partially flatten output.
If shallow_tree
and input_tree
are not sequences, this returns a
single-element list: [input_tree]
.
Use Case:
Sometimes we may wish to partially flatten a nested sequence, retaining some
of the nested structure. We achieve this by specifying a shallow structure,
shallow_tree
, we wish to flatten up to.
The input, input_tree
, can be thought of as having the same structure layout
as shallow_tree
, but with leaf nodes that are themselves tree structures.
Examples:
input_tree = [[[2, 2], [3, 3]], [[4, 9], [5, 5]]]
shallow_tree = [[True, True], [False, True]]
flattened_input_tree = flatten_up_to(shallow_tree, input_tree)
flattened_shallow_tree = flatten_up_to(shallow_tree, shallow_tree)
# Output is:
# [[2, 2], [3, 3], [4, 9], [5, 5]]
# [True, True, False, True]
input_tree = [[('a', 1), [('b', 2), [('c', 3), [('d', 4)]]]]]
shallow_tree = [['level_1', ['level_2', ['level_3', ['level_4']]]]]
input_tree_flattened_as_shallow_tree = flatten_up_to(shallow_tree, input_tree)
input_tree_flattened = flatten(input_tree)
# Output is:
# [('a', 1), ('b', 2), ('c', 3), ('d', 4)]
# ['a', 1, 'b', 2, 'c', 3, 'd', 4]
Non-Sequence Edge Cases:
flatten_up_to(0, 0) # Output: [0]
flatten_up_to(0, [0, 1, 2]) # Output: [[0, 1, 2]]
flatten_up_to([0, 1, 2], 0) # Output: TypeError
flatten_up_to([0, 1, 2], [0, 1, 2]) # Output: [0, 1, 2]
Non-Full-Subtree case:
shallow_tree = ["a", "b"]
input_tree = ["c", ["d", "e"], "f"]
flattened = flatten_up_to(shallow_tree, input_tree,
check_subtrees_length=False)
# Output is:
# ["c", ["d", "e"]]
Args | |
---|---|
shallow_tree
|
a possibly pruned structure of input_tree. |
input_tree
|
an arbitrarily nested structure or a scalar object. Note, numpy arrays are considered scalars. |
check_types
|
bool. If True, check that each node in shallow_tree has the same type as the corresponding node in input_tree. |
expand_composites
|
If true, then composite tensors such as tf.SparseTensor and tf.RaggedTensor are expanded into their component tensors. |
check_subtrees_length
|
if True (default) the subtrees shallow_tree and
input_tree have to be the same length. If False sequences are treated
as key-value like mappings allowing them to be considered as valid
subtrees. Note that this may drop parts of the input_tree .
|
Returns | |
---|---|
A Python list, the partially flattened version of input_tree according to
the structure of shallow_tree .
|
Raises | |
---|---|
TypeError
|
If shallow_tree is a sequence but input_tree is not.
|
TypeError
|
If the sequence types of shallow_tree are different from
input_tree .
|
ValueError
|
If the sequence lengths of shallow_tree are different from
input_tree .
|