def dense_to_sparse_tensor(dense_tensor, ignore_value=None):
"""Converts a dense Tensor to a SparseTensor, dropping ignore_value cells.
Args:
dense_tensor: A `Tensor`.
ignore_value: Entries in `dense_tensor` equal to this value will be
absent from the return `SparseTensor`. If `None`, default value of
dense_tensor's dtype will be used (e.g. '' for `str`, 0 for `int`).
Returns:
A `SparseTensor` with the same shape as `dense_tensor`.
Raises:
ValueError: when `dense_tensor`'s rank is `None`.
"""
with ops.name_scope("DenseToSparseTensor"):
dense_t = ops.convert_to_tensor(dense_tensor)
if dense_t.get_shape().ndims is None:
# TODO(b/32318825): Implement dense_to_sparse_tensor for undefined rank.
raise ValueError("dense_tensor.get_shape() should be defined, got None.")
if ignore_value is None:
if dense_t.dtype == dtypes.string:
# Exception due to TF strings are converted to numpy objects by default.
ignore_value = ""
else:
ignore_value = dense_t.dtype.as_numpy_dtype()
dense_shape = math_ops.cast(array_ops.shape(dense_t), dtypes.int64)
indices = array_ops.where(
math_ops.not_equal(dense_t, math_ops.cast(ignore_value, dense_t.dtype)))
index_dims = len(dense_t.get_shape())
# Flattens the tensor and indices for use with gather.
flat_tensor = array_ops.reshape(dense_t, [-1])
flat_indices = indices[:, index_dims - 1]
# Computes the correct flattened indices for 2d (or higher) tensors.
if index_dims > 1:
higher_dims = indices[:, :index_dims - 1]
shape_multipliers = array_ops.pack(
_multiplier_helper(array_ops.unpack(dense_shape)[1:]))
offsets = math_ops.reduce_sum(
math_ops.mul(higher_dims, shape_multipliers), reduction_indices=[1])
flat_indices = math_ops.add(flat_indices, offsets)
values = array_ops.gather(flat_tensor, flat_indices)
return sparse_tensor.SparseTensor(indices, values, dense_shape)
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