tf.contrib.framework.nest.flatten_with_tuple_paths_up_to

Flattens input_tree up to shallow_tree.

tf.contrib.framework.nest.flatten_with_tuple_paths_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 flattened output.

Returns a list of (path, value) pairs, where value a leaf node in the flattened tree, and path is the tuple path of that leaf in input_tree.

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_with_tuple_paths_up_to(shallow_tree,
                                                      input_tree)
flattened_shallow_tree = flatten_with_tuple_paths_up_to(shallow_tree,
                                                        shallow_tree)

# Output is:
# [((0, 0), [2, 2]),
#  ((0, 1), [3, 3]),
#  ((1, 0), [4, 9]),
#  ((1, 1), [5, 5])]
#
# [((0, 0), True),
#  ((0, 1), True),
#  ((1, 0), False),
#  ((1, 1), 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:
# [((0, 0), ('a', 1)),
#  ((0, 1, 0), ('b', 2)),
#  ((0, 1, 1, 0), ('c', 3)),
#  ((0, 1, 1, 1), ('d', 4))]
# ['a', 1, 'b', 2, 'c', 3, 'd', 4]

Non-Sequence Edge Cases:

flatten_with_tuple_paths_up_to(0, 0)  # Output: [(), 0]

flatten_with_tuple_paths_up_to(0, [0, 1, 2])  # Output: [(), [0, 1, 2]]

flatten_with_tuple_paths_up_to([0, 1, 2], 0)  # Output: TypeError

flatten_with_tuple_paths_up_to([0, 1, 2], [0, 1, 2])
# Output: [((0,) 0), ((1,), 1), ((2,), 2)]

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.