TensorFlow provides several operations to slice or extract parts of a tensor, or join multiple tensors together.
tf.slice(input_, begin, size, name=None)
Extracts a slice from a tensor.
This operation extracts a slice of size size
from a tensor input
starting
at the location specified by begin
. The slice size
is represented as a
tensor shape, where size[i]
is the number of elements of the 'i'th dimension
of input
that you want to slice. The starting location (begin
) for the
slice is represented as an offset in each dimension of input
. In other
words, begin[i]
is the offset into the 'i'th dimension of input
that you
want to slice from.
begin
is zerobased; size
is onebased. If size[i]
is 1,
all remaining elements in dimension i are included in the
slice. In other words, this is equivalent to setting:
size[i] = input.dim_size(i)  begin[i]
This operation requires that:
0 <= begin[i] <= begin[i] + size[i] <= Di for i in [0, n]
For example:
# 'input' is [[[1, 1, 1], [2, 2, 2]],
# [[3, 3, 3], [4, 4, 4]],
# [[5, 5, 5], [6, 6, 6]]]
tf.slice(input, [1, 0, 0], [1, 1, 3]) ==> [[[3, 3, 3]]]
tf.slice(input, [1, 0, 0], [1, 2, 3]) ==> [[[3, 3, 3],
[4, 4, 4]]]
tf.slice(input, [1, 0, 0], [2, 1, 3]) ==> [[[3, 3, 3]],
[[5, 5, 5]]]
Args:
input_
: ATensor
.begin
: Anint32
orint64
Tensor
.size
: Anint32
orint64
Tensor
.name
: A name for the operation (optional).
Returns:
A Tensor
the same type as input
.
tf.strided_slice(input_, begin, end, strides, begin_mask=0, end_mask=0, ellipsis_mask=0, new_axis_mask=0, shrink_axis_mask=0, name=None)
Extracts a strided slice from a tensor.
To a first order, this operation extracts a slice of size end  begin
from a tensor input
starting at the location specified by begin
. The slice continues by adding
stride
to the begin
index until all dimensions are not less than end
.
Note that components of stride can be negative, which causes a reverse
slice.
This operation can be thought of an encoding of a numpy style sliced
range. Given a python slice input[
begin
, end
, and strides
will be all length n. n is in general
not the same dimensionality as input
.
For the ith spec,
begin_mask
, end_mask
, ellipsis_mask
, new_axis_mask
,
and shrink_axis_mask
will have the ith bit corrsponding to
the ith spec.
If the ith bit of begin_mask
is nonzero, begin[i]
is ignored and
the fullest possible range in that dimension is used instead.
end_mask
works analogously, except with the end range.
foo[5:,:,:3]
on a 7x8x9 tensor is equivalent to foo[5:7,0:8,0:3]
.
foo[::1]
reverses a tensor with shape 8.
If the ith bit of ellipsis_mask
, as many unspecified dimensions
as needed will be inserted between other dimensions. Only one
nonzero bit is allowed in ellipsis_mask
.
For example foo[3:5,...,4:5]
on a shape 10x3x3x10 tensor is
equivalent to foo[3:5,:,:,4:5]
and
foo[3:5,...]
is equivalent to foo[3:5,:,:,:]
.
If the ith bit of new_axis_mask
is one, then a begin
,
end
, and stride
are ignored and a new length 1 dimension is
added at this point in the output tensor.
For example foo[3:5,4]
on a 10x8 tensor produces a shape 2 tensor
whereas foo[3:5,4:5]
produces a shape 2x1 tensor with shrink_mask
being 1<<1 == 2.
If the ith bit of shrink_axis_mask
is one, then begin
,
end[i]
, and stride[i]
are used to do a slice in the appropriate
dimension, but the output tensor will be reduced in dimensionality
by one. This is only valid if the ith entry of slice[i]==1.
NOTE: begin
and end
are zeroindexed.
strides` entries must be nonzero.
# 'input' is [[[1, 1, 1], [2, 2, 2]],
# [[3, 3, 3], [4, 4, 4]],
# [[5, 5, 5], [6, 6, 6]]]
tf.slice(input, [1, 0, 0], [2, 1, 3], [1, 1, 1]) ==> [[[3, 3, 3]]]
tf.slice(input, [1, 0, 0], [2, 2, 3], [1, 1, 1]) ==> [[[3, 3, 3],
[4, 4, 4]]]
tf.slice(input, [1, 1, 0], [2, 1, 3], [1, 1, 1]) ==>[[[4, 4, 4],
[3, 3, 3]]]
Args:
input_
: ATensor
.begin
: Anint32
orint64
Tensor
.end
: Anint32
orint64
Tensor
.strides
: Anint32
orint64
Tensor
.begin_mask
: Anint32
mask.end_mask
: Anint32
mask.ellipsis_mask
: Anint32
mask.new_axis_mask
: Anint32
mask.shrink_axis_mask
: Anint32
mask.name
: A name for the operation (optional).
Returns:
A Tensor
the same type as input
.
tf.split(split_dim, num_split, value, name='split')
Splits a tensor into num_split
tensors along one dimension.
Splits value
along dimension split_dim
into num_split
smaller tensors.
Requires that num_split
evenly divide value.shape[split_dim]
.
For example:
# 'value' is a tensor with shape [5, 30]
# Split 'value' into 3 tensors along dimension 1
split0, split1, split2 = tf.split(1, 3, value)
tf.shape(split0) ==> [5, 10]
num_items = t.get_shape()[axis].value
[tf.squeeze(s, [axis]) for s in tf.split(axis, num_items, t)]
can be rewritten as
tf.unpack(t, axis=axis)
Args:
split_dim
: A 0Dint32
Tensor
. The dimension along which to split. Must be in the range[0, rank(value))
.num_split
: A Python integer. The number of ways to split.value
: TheTensor
to split.name
: A name for the operation (optional).
Returns:
num_split
Tensor
objects resulting from splitting value
.
tf.tile(input, multiples, name=None)
Constructs a tensor by tiling a given tensor.
This operation creates a new tensor by replicating input
multiples
times.
The output tensor's i'th dimension has input.dims(i) * multiples[i]
elements,
and the values of input
are replicated multiples[i]
times along the 'i'th
dimension. For example, tiling [a b c d]
by [2]
produces
[a b c d a b c d]
.
Args:
input
: ATensor
. 1D or higher.multiples
: ATensor
of typeint32
. 1D. Length must be the same as the number of dimensions ininput
name
: A name for the operation (optional).
Returns:
A Tensor
. Has the same type as input
.
tf.pad(tensor, paddings, mode='CONSTANT', name=None)
Pads a tensor.
This operation pads a tensor
according to the paddings
you specify.
paddings
is an integer tensor with shape [n, 2]
, where n is the rank of
tensor
. For each dimension D of input
, paddings[D, 0]
indicates how
many values to add before the contents of tensor
in that dimension, and
paddings[D, 1]
indicates how many values to add after the contents of
tensor
in that dimension. If mode
is "REFLECT" then both paddings[D, 0]
and paddings[D, 1]
must be no greater than tensor.dim_size(D)  1
. If
mode
is "SYMMETRIC" then both paddings[D, 0]
and paddings[D, 1]
must be
no greater than tensor.dim_size(D)
.
The padded size of each dimension D of the output is:
paddings[D, 0] + tensor.dim_size(D) + paddings[D, 1]
For example:
# 't' is [[1, 2, 3], [4, 5, 6]].
# 'paddings' is [[1, 1,], [2, 2]].
# rank of 't' is 2.
pad(t, paddings, "CONSTANT") ==> [[0, 0, 0, 0, 0, 0, 0],
[0, 0, 1, 2, 3, 0, 0],
[0, 0, 4, 5, 6, 0, 0],
[0, 0, 0, 0, 0, 0, 0]]
pad(t, paddings, "REFLECT") ==> [[6, 5, 4, 5, 6, 5, 4],
[3, 2, 1, 2, 3, 2, 1],
[6, 5, 4, 5, 6, 5, 4],
[3, 2, 1, 2, 3, 2, 1]]
pad(t, paddings, "SYMMETRIC") ==> [[2, 1, 1, 2, 3, 3, 2],
[2, 1, 1, 2, 3, 3, 2],
[5, 4, 4, 5, 6, 6, 5],
[5, 4, 4, 5, 6, 6, 5]]
Args:
tensor
: ATensor
.paddings
: ATensor
of typeint32
.mode
: One of "CONSTANT", "REFLECT", or "SYMMETRIC".name
: A name for the operation (optional).
Returns:
A Tensor
. Has the same type as tensor
.
Raises:
ValueError
: When mode is not one of "CONSTANT", "REFLECT", or "SYMMETRIC".
tf.concat(concat_dim, values, name='concat')
Concatenates tensors along one dimension.
Concatenates the list of tensors values
along dimension concat_dim
. If
values[i].shape = [D0, D1, ... Dconcat_dim(i), ...Dn]
, the concatenated
result has shape
[D0, D1, ... Rconcat_dim, ...Dn]
where
Rconcat_dim = sum(Dconcat_dim(i))
That is, the data from the input tensors is joined along the concat_dim
dimension.
The number of dimensions of the input tensors must match, and all dimensions
except concat_dim
must be equal.
For example:
t1 = [[1, 2, 3], [4, 5, 6]]
t2 = [[7, 8, 9], [10, 11, 12]]
tf.concat(0, [t1, t2]) ==> [[1, 2, 3], [4, 5, 6], [7, 8, 9], [10, 11, 12]]
tf.concat(1, [t1, t2]) ==> [[1, 2, 3, 7, 8, 9], [4, 5, 6, 10, 11, 12]]
# tensor t3 with shape [2, 3]
# tensor t4 with shape [2, 3]
tf.shape(tf.concat(0, [t3, t4])) ==> [4, 3]
tf.shape(tf.concat(1, [t3, t4])) ==> [2, 6]
tf.concat(axis, [tf.expand_dims(t, axis) for t in tensors])
can be rewritten as
tf.pack(tensors, axis=axis)
Args:
concat_dim
: 0Dint32
Tensor
. Dimension along which to concatenate.values
: A list ofTensor
objects or a singleTensor
.name
: A name for the operation (optional).
Returns:
A Tensor
resulting from concatenation of the input tensors.
tf.pack(values, axis=0, name='pack')
Packs a list of rankR
tensors into one rank(R+1)
tensor.
Packs the list of tensors in values
into a tensor with rank one higher than
each tensor in values
, by packing them along the axis
dimension.
Given a list of length N
of tensors of shape (A, B, C)
;
if axis == 0
then the output
tensor will have the shape (N, A, B, C)
.
if axis == 1
then the output
tensor will have the shape (A, N, B, C)
.
Etc.
For example:
# 'x' is [1, 4]
# 'y' is [2, 5]
# 'z' is [3, 6]
pack([x, y, z]) => [[1, 4], [2, 5], [3, 6]] # Pack along first dim.
pack([x, y, z], axis=1) => [[1, 2, 3], [4, 5, 6]]
This is the opposite of unpack. The numpy equivalent is
tf.pack([x, y, z]) = np.asarray([x, y, z])
Args:
values
: A list ofTensor
objects with the same shape and type.axis
: Anint
. The axis to pack along. Defaults to the first dimension. Supports negative indexes.name
: A name for this operation (optional).
Returns:
output
: A packedTensor
with the same type asvalues
.
Raises:
ValueError
: Ifaxis
is out of the range [(R+1), R+1).
tf.unpack(value, num=None, axis=0, name='unpack')
Unpacks the given dimension of a rankR
tensor into rank(R1)
tensors.
Unpacks num
tensors from value
by chipping it along the axis
dimension.
If num
is not specified (the default), it is inferred from value
's shape.
If value.shape[axis]
is not known, ValueError
is raised.
For example, given a tensor of shape (A, B, C, D)
;
If axis == 0
then the i'th tensor in output
is the slice
value[i, :, :, :]
and each tensor in output
will have shape (B, C, D)
.
(Note that the dimension unpacked along is gone, unlike split
).
If axis == 1
then the i'th tensor in output
is the slice
value[:, i, :, :]
and each tensor in output
will have shape (A, C, D)
.
Etc.
This is the opposite of pack. The numpy equivalent is
tf.unpack(x, n) = list(x)
Args:
value
: A rankR > 0
Tensor
to be unpacked.num
: Anint
. The length of the dimensionaxis
. Automatically inferred ifNone
(the default).axis
: Anint
. The axis to unpack along. Defaults to the first dimension. Supports negative indexes.name
: A name for the operation (optional).
Returns:
The list of Tensor
objects unpacked from value
.
Raises:
ValueError
: Ifnum
is unspecified and cannot be inferred.ValueError
: Ifaxis
is out of the range [R, R).
tf.reverse_sequence(input, seq_lengths, seq_dim, batch_dim=None, name=None)
Reverses variable length slices.
This op first slices input
along the dimension batch_dim
, and for each
slice i
, reverses the first seq_lengths[i]
elements along
the dimension seq_dim
.
The elements of seq_lengths
must obey seq_lengths[i] < input.dims[seq_dim]
,
and seq_lengths
must be a vector of length input.dims[batch_dim]
.
The output slice i
along dimension batch_dim
is then given by input
slice i
, with the first seq_lengths[i]
slices along dimension
seq_dim
reversed.
For example:
# Given this:
batch_dim = 0
seq_dim = 1
input.dims = (4, 8, ...)
seq_lengths = [7, 2, 3, 5]
# then slices of input are reversed on seq_dim, but only up to seq_lengths:
output[0, 0:7, :, ...] = input[0, 7:0:1, :, ...]
output[1, 0:2, :, ...] = input[1, 2:0:1, :, ...]
output[2, 0:3, :, ...] = input[2, 3:0:1, :, ...]
output[3, 0:5, :, ...] = input[3, 5:0:1, :, ...]
# while entries past seq_lens are copied through:
output[0, 7:, :, ...] = input[0, 7:, :, ...]
output[1, 2:, :, ...] = input[1, 2:, :, ...]
output[2, 3:, :, ...] = input[2, 3:, :, ...]
output[3, 2:, :, ...] = input[3, 2:, :, ...]
In contrast, if:
# Given this:
batch_dim = 2
seq_dim = 0
input.dims = (8, ?, 4, ...)
seq_lengths = [7, 2, 3, 5]
# then slices of input are reversed on seq_dim, but only up to seq_lengths:
output[0:7, :, 0, :, ...] = input[7:0:1, :, 0, :, ...]
output[0:2, :, 1, :, ...] = input[2:0:1, :, 1, :, ...]
output[0:3, :, 2, :, ...] = input[3:0:1, :, 2, :, ...]
output[0:5, :, 3, :, ...] = input[5:0:1, :, 3, :, ...]
# while entries past seq_lens are copied through:
output[7:, :, 0, :, ...] = input[7:, :, 0, :, ...]
output[2:, :, 1, :, ...] = input[2:, :, 1, :, ...]
output[3:, :, 2, :, ...] = input[3:, :, 2, :, ...]
output[2:, :, 3, :, ...] = input[2:, :, 3, :, ...]
Args:
input
: ATensor
. The input to reverse.seq_lengths
: ATensor
of typeint64
. 1D with lengthinput.dims(batch_dim)
andmax(seq_lengths) < input.dims(seq_dim)
seq_dim
: Anint
. The dimension which is partially reversed.batch_dim
: An optionalint
. Defaults to0
. The dimension along which reversal is performed.name
: A name for the operation (optional).
Returns:
A Tensor
. Has the same type as input
.
The partially reversed input. It has the same shape as input
.
tf.reverse(tensor, dims, name=None)
Reverses specific dimensions of a tensor.
Given a tensor
, and a bool
tensor dims
representing the dimensions
of tensor
, this operation reverses each dimension i of tensor
where
dims[i]
is True
.
tensor
can have up to 8 dimensions. The number of dimensions
of tensor
must equal the number of elements in dims
. In other words:
rank(tensor) = size(dims)
For example:
# tensor 't' is [[[[ 0, 1, 2, 3],
# [ 4, 5, 6, 7],
# [ 8, 9, 10, 11]],
# [[12, 13, 14, 15],
# [16, 17, 18, 19],
# [20, 21, 22, 23]]]]
# tensor 't' shape is [1, 2, 3, 4]
# 'dims' is [False, False, False, True]
reverse(t, dims) ==> [[[[ 3, 2, 1, 0],
[ 7, 6, 5, 4],
[ 11, 10, 9, 8]],
[[15, 14, 13, 12],
[19, 18, 17, 16],
[23, 22, 21, 20]]]]
# 'dims' is [False, True, False, False]
reverse(t, dims) ==> [[[[12, 13, 14, 15],
[16, 17, 18, 19],
[20, 21, 22, 23]
[[ 0, 1, 2, 3],
[ 4, 5, 6, 7],
[ 8, 9, 10, 11]]]]
# 'dims' is [False, False, True, False]
reverse(t, dims) ==> [[[[8, 9, 10, 11],
[4, 5, 6, 7],
[0, 1, 2, 3]]
[[20, 21, 22, 23],
[16, 17, 18, 19],
[12, 13, 14, 15]]]]
Args:
tensor
: ATensor
. Must be one of the following types:uint8
,int8
,int32
,bool
,half
,float32
,float64
,complex64
,complex128
. Up to 8D.dims
: ATensor
of typebool
. 1D. The dimensions to reverse.name
: A name for the operation (optional).
Returns:
A Tensor
. Has the same type as tensor
. The same shape as tensor
.
tf.transpose(a, perm=None, name='transpose')
Transposes a
. Permutes the dimensions according to perm
.
The returned tensor's dimension i will correspond to the input dimension
perm[i]
. If perm
is not given, it is set to (n1...0), where n is
the rank of the input tensor. Hence by default, this operation performs a
regular matrix transpose on 2D input Tensors.
For example:
# 'x' is [[1 2 3]
# [4 5 6]]
tf.transpose(x) ==> [[1 4]
[2 5]
[3 6]]
# Equivalently
tf.transpose(x, perm=[1, 0]) ==> [[1 4]
[2 5]
[3 6]]
# 'perm' is more useful for ndimensional tensors, for n > 2
# 'x' is [[[1 2 3]
# [4 5 6]]
# [[7 8 9]
# [10 11 12]]]
# Take the transpose of the matrices in dimension0
tf.transpose(x, perm=[0, 2, 1]) ==> [[[1 4]
[2 5]
[3 6]]
[[7 10]
[8 11]
[9 12]]]
Args:
a
: ATensor
.perm
: A permutation of the dimensions ofa
.name
: A name for the operation (optional).
Returns:
A transposed Tensor
.
tf.extract_image_patches(images, ksizes, strides, rates, padding, name=None)
Extract patches
from images
and put them in the "depth" output dimension.
Args:
images
: ATensor
. Must be one of the following types:float32
,float64
,int32
,int64
,uint8
,int16
,int8
,uint16
,half
. 4D Tensor with shape[batch, in_rows, in_cols, depth]
.ksizes
: A list ofints
that has length>= 4
. The size of the sliding window for each dimension ofimages
.strides
: A list ofints
that has length>= 4
. 1D of length 4. How far the centers of two consecutive patches are in the images. Must be:[1, stride_rows, stride_cols, 1]
.rates
: A list ofints
that has length>= 4
. 1D of length 4. Must be:[1, rate_rows, rate_cols, 1]
. This is the input stride, specifying how far two consecutive patch samples are in the input. Equivalent to extracting patches withpatch_sizes_eff = patch_sizes + (patch_sizes  1) * (rates  1), followed by subsampling them spatially by a factor of
rates`.
padding
: Astring
from:"SAME", "VALID"
. The type of padding algorithm to use.We specify the sizerelated attributes as:
ksizes = [1, ksize_rows, ksize_cols, 1] strides = [1, strides_rows, strides_cols, 1] rates = [1, rates_rows, rates_cols, 1]

name
: A name for the operation (optional).
Returns:
A Tensor
. Has the same type as images
.
4D Tensor with shape [batch, out_rows, out_cols, ksize_rows *
ksize_cols * depth]
containing image patches with size
ksize_rows x ksize_cols x depth
vectorized in the "depth" dimension.
tf.space_to_batch(input, paddings, block_size, name=None)
SpaceToBatch for 4D tensors of type T.
Zeropads and then rearranges (permutes) blocks of spatial data into batch.
More specifically, this op outputs a copy of the input tensor where values from
the height
and width
dimensions are moved to the batch
dimension. After
the zeropadding, both height
and width
of the input must be divisible by the
block size.
Args:
input
: ATensor
. 4D with shape[batch, height, width, depth]
.
paddings
: ATensor
of typeint32
. 2D tensor of nonnegative integers with shape[2, 2]
. It specifies the padding of the input with zeros across the spatial dimensions as follows:paddings = [[pad_top, pad_bottom], [pad_left, pad_right]]
The effective spatial dimensions of the zeropadded input tensor will be:
height_pad = pad_top + height + pad_bottom width_pad = pad_left + width + pad_right
The attr
block_size
must be greater than one. It indicates the block size. Nonoverlapping blocks of size
block_size x block size
in the height and width dimensions are rearranged into the batch dimension at each location.  The batch of the output tensor is
batch * block_size * block_size
.  Both height_pad and width_pad must be divisible by block_size.
The shape of the output will be:
[batch*block_size*block_size, height_pad/block_size, width_pad/block_size, depth]
Some examples:
(1) For the following input of shape
[1, 2, 2, 1]
and block_size of 2:prettyprint x = [[[[1], [2]], [[3], [4]]]]
The output tensor has shape
[4, 1, 1, 1]
and value:prettyprint [[[[1]]], [[[2]]], [[[3]]], [[[4]]]]
(2) For the following input of shape
[1, 2, 2, 3]
and block_size of 2:prettyprint x = [[[[1, 2, 3], [4, 5, 6]], [[7, 8, 9], [10, 11, 12]]]]
The output tensor has shape
[4, 1, 1, 3]
and value:prettyprint [[[1, 2, 3]], [[4, 5, 6]], [[7, 8, 9]], [[10, 11, 12]]]
(3) For the following input of shape
[1, 4, 4, 1]
and block_size of 2:prettyprint x = [[[[1], [2], [3], [4]], [[5], [6], [7], [8]], [[9], [10], [11], [12]], [[13], [14], [15], [16]]]]
The output tensor has shape
[4, 2, 2, 1]
and value:prettyprint x = [[[[1], [3]], [[5], [7]]], [[[2], [4]], [[10], [12]]], [[[5], [7]], [[13], [15]]], [[[6], [8]], [[14], [16]]]]
(4) For the following input of shape
[2, 2, 4, 1]
and block_size of 2:prettyprint x = [[[[1], [2], [3], [4]], [[5], [6], [7], [8]]], [[[9], [10], [11], [12]], [[13], [14], [15], [16]]]]
The output tensor has shape
[8, 1, 2, 1]
and value:prettyprint x = [[[[1], [3]]], [[[9], [11]]], [[[2], [4]]], [[[10], [12]]], [[[5], [7]]], [[[13], [15]]], [[[6], [8]]], [[[14], [16]]]]
Among others, this operation is useful for reducing atrous convolution into regular convolution.
 Nonoverlapping blocks of size

block_size
: Anint
that is>= 2
. name
: A name for the operation (optional).
Returns:
A Tensor
. Has the same type as input
.
tf.batch_to_space(input, crops, block_size, name=None)
BatchToSpace for 4D tensors of type T.
Rearranges (permutes) data from batch into blocks of spatial data, followed by
cropping. This is the reverse transformation of SpaceToBatch. More specifically,
this op outputs a copy of the input tensor where values from the batch
dimension are moved in spatial blocks to the height
and width
dimensions,
followed by cropping along the height
and width
dimensions.
Args:
input
: ATensor
. 4D tensor with shape[batch*block_size*block_size, height_pad/block_size, width_pad/block_size, depth]
. Note that the batch size of the input tensor must be divisible byblock_size * block_size
.
crops
: ATensor
of typeint32
. 2D tensor of nonnegative integers with shape[2, 2]
. It specifies how many elements to crop from the intermediate result across the spatial dimensions as follows:crops = [[crop_top, crop_bottom], [crop_left, crop_right]]

block_size
: Anint
that is>= 2
. name
: A name for the operation (optional).
Returns:
A Tensor
. Has the same type as input
.
4D with shape [batch, height, width, depth]
, where:
height = height_pad  crop_top  crop_bottom
width = width_pad  crop_left  crop_right
The attr block_size
must be greater than one. It indicates the block size.
Some examples:
(1) For the following input of shape [4, 1, 1, 1]
and block_size of 2:
prettyprint
[[[[1]]], [[[2]]], [[[3]]], [[[4]]]]
The output tensor has shape [1, 2, 2, 1]
and value:
prettyprint
x = [[[[1], [2]], [[3], [4]]]]
(2) For the following input of shape [4, 1, 1, 3]
and block_size of 2:
prettyprint
[[[1, 2, 3]], [[4, 5, 6]], [[7, 8, 9]], [[10, 11, 12]]]
The output tensor has shape [1, 2, 2, 3]
and value:
prettyprint
x = [[[[1, 2, 3], [4, 5, 6]],
[[7, 8, 9], [10, 11, 12]]]]
(3) For the following input of shape [4, 2, 2, 1]
and block_size of 2:
prettyprint
x = [[[[1], [3]], [[5], [7]]],
[[[2], [4]], [[10], [12]]],
[[[5], [7]], [[13], [15]]],
[[[6], [8]], [[14], [16]]]]
The output tensor has shape [1, 4, 4, 1]
and value:
prettyprint
x = [[[1], [2], [3], [4]],
[[5], [6], [7], [8]],
[[9], [10], [11], [12]],
[[13], [14], [15], [16]]]
(4) For the following input of shape [8, 1, 2, 1]
and block_size of 2:
prettyprint
x = [[[[1], [3]]], [[[9], [11]]], [[[2], [4]]], [[[10], [12]]],
[[[5], [7]]], [[[13], [15]]], [[[6], [8]]], [[[14], [16]]]]
The output tensor has shape [2, 2, 4, 1]
and value:
prettyprint
x = [[[[1], [3]], [[5], [7]]],
[[[2], [4]], [[10], [12]]],
[[[5], [7]], [[13], [15]]],
[[[6], [8]], [[14], [16]]]]
tf.space_to_depth(input, block_size, name=None)
SpaceToDepth for tensors of type T.
Rearranges blocks of spatial data, into depth. More specifically,
this op outputs a copy of the input tensor where values from the height
and width
dimensions are moved to the depth
dimension.
The attr block_size
indicates the input block size and how the data is moved.
 Nonoverlapping blocks of size
block_size x block size
are rearranged into depth at each location.  The depth of the output tensor is
input_depth * block_size * block_size
.  The input tensor's height and width must be divisible by block_size.
That is, assuming the input is in the shape:
[batch, height, width, depth]
,
the shape of the output will be:
[batch, height/block_size, width/block_size, depth*block_size*block_size]
This operation requires that the input tensor be of rank 4, and that
block_size
be >=1 and a divisor of both the input height
and width
.
This operation is useful for resizing the activations between convolutions (but keeping all data), e.g. instead of pooling. It is also useful for training purely convolutional models.
For example, given this input of shape [1, 2, 2, 1]
, and block_size of 2:
x = [[[[1], [2]],
[[3], [4]]]]
This operation will output a tensor of shape [1, 1, 1, 4]
:
[[[[1, 2, 3, 4]]]]
Here, the input has a batch of 1 and each batch element has shape [2, 2, 1]
,
the corresponding output will have a single element (i.e. width and height are
both 1) and will have a depth of 4 channels (1 * block_size * block_size).
The output element shape is [1, 1, 4]
.
For an input tensor with larger depth, here of shape [1, 2, 2, 3]
, e.g.
x = [[[[1, 2, 3], [4, 5, 6]],
[[7, 8, 9], [10, 11, 12]]]]
This operation, for block_size of 2, will return the following tensor of shape
[1, 1, 1, 12]
[[[[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12]]]]
Similarly, for the following input of shape [1 4 4 1]
, and a block size of 2:
x = [[[[1], [2], [5], [6]],
[[3], [4], [7], [8]],
[[9], [10], [13], [14]],
[[11], [12], [15], [16]]]]
the operator will return the following tensor of shape [1 2 2 4]
:
x = [[[[1, 2, 3, 4],
[5, 6, 7, 8]],
[[9, 10, 11, 12],
[13, 14, 15, 16]]]]
Args:
input
: ATensor
.block_size
: Anint
that is>= 2
. The size of the spatial block.name
: A name for the operation (optional).
Returns:
A Tensor
. Has the same type as input
.
tf.depth_to_space(input, block_size, name=None)
DepthToSpace for tensors of type T.
Rearranges data from depth into blocks of spatial data.
This is the reverse transformation of SpaceToDepth. More specifically,
this op outputs a copy of the input tensor where values from the depth
dimension are moved in spatial blocks to the height
and width
dimensions.
The attr block_size
indicates the input block size and how the data is moved.
 Chunks of data of size
block_size * block_size
from depth are rearranged into nonoverlapping blocks of sizeblock_size x block_size
 The width the output tensor is
input_depth * block_size
, whereas the height isinput_height * block_size
.  The depth of the input tensor must be divisible by
block_size * block_size
.
That is, assuming the input is in the shape:
[batch, height, width, depth]
,
the shape of the output will be:
[batch, height*block_size, width*block_size, depth/(block_size*block_size)]
This operation requires that the input tensor be of rank 4, and that
block_size
be >=1 and that block_size * block_size
be a divisor of the
input depth.
This operation is useful for resizing the activations between convolutions (but keeping all data), e.g. instead of pooling. It is also useful for training purely convolutional models.
For example, given this input of shape [1, 1, 1, 4]
, and a block size of 2:
x = [[[[1, 2, 3, 4]]]]
This operation will output a tensor of shape [1, 2, 2, 1]
:
[[[[1], [2]],
[[3], [4]]]]
Here, the input has a batch of 1 and each batch element has shape [1, 1, 4]
,
the corresponding output will have 2x2 elements and will have a depth of
1 channel (1 = 4 / (block_size * block_size)
).
The output element shape is [2, 2, 1]
.
For an input tensor with larger depth, here of shape [1, 1, 1, 12]
, e.g.
x = [[[[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12]]]]
This operation, for block size of 2, will return the following tensor of shape
[1, 2, 2, 3]
[[[[1, 2, 3], [4, 5, 6]],
[[7, 8, 9], [10, 11, 12]]]]
Similarly, for the following input of shape [1 2 2 4]
, and a block size of 2:
x = [[[[1, 2, 3, 4],
[5, 6, 7, 8]],
[[9, 10, 11, 12],
[13, 14, 15, 16]]]]
the operator will return the following tensor of shape [1 4 4 1]
:
x = [[ [1], [2], [5], [6]],
[ [3], [4], [7], [8]],
[ [9], [10], [13], [14]],
[ [11], [12], [15], [16]]]
Args:
input
: ATensor
.block_size
: Anint
that is>= 2
. The size of the spatial block, same as in Space2Depth.name
: A name for the operation (optional).
Returns:
A Tensor
. Has the same type as input
.
tf.gather(params, indices, validate_indices=None, name=None)
Gather slices from params
according to indices
.
indices
must be an integer tensor of any dimension (usually 0D or 1D).
Produces an output tensor with shape indices.shape + params.shape[1:]
where:
# Scalar indices
output[:, ..., :] = params[indices, :, ... :]
# Vector indices
output[i, :, ..., :] = params[indices[i], :, ... :]
# Higher rank indices
output[i, ..., j, :, ... :] = params[indices[i, ..., j], :, ..., :]
If indices
is a permutation and len(indices) == params.shape[0]
then
this operation will permute params
accordingly.
Args:
params
: ATensor
.indices
: ATensor
. Must be one of the following types:int32
,int64
.validate_indices
: An optionalbool
. Defaults toTrue
.name
: A name for the operation (optional).
Returns:
A Tensor
. Has the same type as params
.
tf.gather_nd(params, indices, name=None)
Gather values or slices from params
according to indices
.
params
is a Tensor of rank R
and indices
is a Tensor of rank M
.
indices
must be integer tensor, containing indices into params
.
It must be shape [d_0, ..., d_N, R]
where 0 < R <= M
.
The innermost dimension of indices
(with length R
) corresponds to
indices into elements (if R = M
) or slices (if R < M
) along the N
th
dimension of params
.
Produces an output tensor with shape
[d_0, ..., d_{n1}, params.shape[R], ..., params.shape[M1]].
Some examples below.
Simple indexing into a matrix:
indices = [[0, 0], [1, 1]]
params = [['a', 'b'], ['c', 'd']]
output = ['a', 'd']
Slice indexing into a matrix:
indices = [[1], [0]]
params = [['a', 'b'], ['c', 'd']]
output = [['c', 'd'], ['a', 'b']]
Indexing into a 3tensor:
indices = [[1]]
params = [[['a0', 'b0'], ['c0', 'd0']],
[['a1', 'b1'], ['c1', 'd1']]]
output = [[['a1', 'b1'], ['c1', 'd1']]]
indices = [[0, 1], [1, 0]]
params = [[['a0', 'b0'], ['c0', 'd0']],
[['a1', 'b1'], ['c1', 'd1']]]
output = [['c0', 'd0'], ['a1', 'b1']]
indices = [[0, 0, 1], [1, 0, 1]]
params = [[['a0', 'b0'], ['c0', 'd0']],
[['a1', 'b1'], ['c1', 'd1']]]
output = ['b0', 'b1']
Batched indexing into a matrix:
indices = [[[0, 0]], [[0, 1]]]
params = [['a', 'b'], ['c', 'd']]
output = [['a'], ['b']]
Batched slice indexing into a matrix:
indices = [[[1]], [[0]]]
params = [['a', 'b'], ['c', 'd']]
output = [[['c', 'd']], [['a', 'b']]]
Batched indexing into a 3tensor:
indices = [[[1]], [[0]]]
params = [[['a0', 'b0'], ['c0', 'd0']],
[['a1', 'b1'], ['c1', 'd1']]]
output = [[[['a1', 'b1'], ['c1', 'd1']]],
[[['a0', 'b0'], ['c0', 'd0']]]]
indices = [[[0, 1], [1, 0]], [[0, 0], [1, 1]]]
params = [[['a0', 'b0'], ['c0', 'd0']],
[['a1', 'b1'], ['c1', 'd1']]]
output = [[['c0', 'd0'], ['a1', 'b1']],
[['a0', 'b0'], ['c1', 'd1']]]
indices = [[[0, 0, 1], [1, 0, 1]], [[0, 1, 1], [1, 1, 0]]]
params = [[['a0', 'b0'], ['c0', 'd0']],
[['a1', 'b1'], ['c1', 'd1']]]
output = [['b0', 'b1'], ['d0', 'c1']]
Args:
params
: ATensor
.MD
. The tensor from which to gather values.indices
: ATensor
. Must be one of the following types:int32
,int64
.(N+1)D
. Index tensor having shape[d_0, ..., d_N, R]
.name
: A name for the operation (optional).
Returns:
A Tensor
. Has the same type as params
.
(N+MR)D
. Values from params
gathered from indices given by
indices
.
tf.dynamic_partition(data, partitions, num_partitions, name=None)
Partitions data
into num_partitions
tensors using indices from partitions
.
For each index tuple js
of size partitions.ndim
, the slice data[js, ...]
becomes part of outputs[partitions[js]]
. The slices with partitions[js] = i
are placed in outputs[i]
in lexicographic order of js
, and the first
dimension of outputs[i]
is the number of entries in partitions
equal to i
.
In detail,
outputs[i].shape = [sum(partitions == i)] + data.shape[partitions.ndim:]
outputs[i] = pack([data[js, ...] for js if partitions[js] == i])
data.shape
must start with partitions.shape
.
For example:
# Scalar partitions
partitions = 1
num_partitions = 2
data = [10, 20]
outputs[0] = [] # Empty with shape [0, 2]
outputs[1] = [[10, 20]]
# Vector partitions
partitions = [0, 0, 1, 1, 0]
num_partitions = 2
data = [10, 20, 30, 40, 50]
outputs[0] = [10, 20, 50]
outputs[1] = [30, 40]
Args:
data
: ATensor
.partitions
: ATensor
of typeint32
. Any shape. Indices in the range[0, num_partitions)
.num_partitions
: Anint
that is>= 1
. The number of partitions to output.name
: A name for the operation (optional).
Returns:
A list of num_partitions
Tensor
objects of the same type as data.
tf.dynamic_stitch(indices, data, name=None)
Interleave the values from the data
tensors into a single tensor.
Builds a merged tensor such that
merged[indices[m][i, ..., j], ...] = data[m][i, ..., j, ...]
For example, if each indices[m]
is scalar or vector, we have
# Scalar indices
merged[indices[m], ...] = data[m][...]
# Vector indices
merged[indices[m][i], ...] = data[m][i, ...]
Each data[i].shape
must start with the corresponding indices[i].shape
,
and the rest of data[i].shape
must be constant w.r.t. i
. That is, we
must have data[i].shape = indices[i].shape + constant
. In terms of this
constant
, the output shape is
merged.shape = [max(indices)] + constant
Values are merged in order, so if an index appears in both indices[m][i]
and
indices[n][j]
for (m,i) < (n,j)
the slice data[n][j]
will appear in the
merged result.
For example:
indices[0] = 6
indices[1] = [4, 1]
indices[2] = [[5, 2], [0, 3]]
data[0] = [61, 62]
data[1] = [[41, 42], [11, 12]]
data[2] = [[[51, 52], [21, 22]], [[1, 2], [31, 32]]]
merged = [[1, 2], [11, 12], [21, 22], [31, 32], [41, 42],
[51, 52], [61, 62]]
Args:
indices
: A list of at least 2Tensor
objects of typeint32
.data
: A list with the same number ofTensor
objects asindices
ofTensor
objects of the same type.name
: A name for the operation (optional).
Returns:
A Tensor
. Has the same type as data
.
tf.boolean_mask(tensor, mask, name='boolean_mask')
Apply boolean mask to tensor. Numpy equivalent is tensor[mask]
.
# 1D example
tensor = [0, 1, 2, 3]
mask = [True, False, True, False]
boolean_mask(tensor, mask) ==> [0, 2]
In general, 0 < dim(mask) = K <= dim(tensor)
, and mask
's shape must match
the first K dimensions of tensor
's shape. We then have:
boolean_mask(tensor, mask)[i, j1,...,jd] = tensor[i1,...,iK,j1,...,jd]
where (i1,...,iK)
is the ith True
entry of mask
(rowmajor order).
Args:
tensor
: ND tensor.mask
: KD boolean tensor, K <= N and K must be known statically.name
: A name for this operation (optional).
Returns:
Tensor populated by entries in tensor
corresponding to True
values in
mask
.
Raises:

ValueError
: If shapes do not conform. 
Examples
:
# 2D example
tensor = [[1, 2], [3, 4], [5, 6]]
mask = [True, False, True]
boolean_mask(tensor, mask) ==> [[1, 2], [5, 6]]
tf.one_hot(indices, depth, on_value=None, off_value=None, axis=None, dtype=None, name=None)
Returns a onehot tensor.
The locations represented by indices in indices
take value on_value
,
while all other locations take value off_value
.
on_value
and off_value
must have matching data types. If dtype
is also
provided, they must be the same data type as specified by dtype
.
If on_value
is not provided, it will default to the value 1
with type
dtype
If off_value
is not provided, it will default to the value 0
with type
dtype
If the input indices
is rank N
, the output will have rank N+1
. The
new axis is created at dimension axis
(default: the new axis is appended
at the end).
If indices
is a scalar the output shape will be a vector of length depth
If indices
is a vector of length features
, the output shape will be:
features x depth if axis == 1
depth x features if axis == 0
If indices
is a matrix (batch) with shape [batch, features]
, the output
shape will be:
batch x features x depth if axis == 1
batch x depth x features if axis == 1
depth x batch x features if axis == 0
If dtype
is not provided, it will attempt to assume the data type of
on_value
or off_value
, if one or both are passed in. If none of
on_value
, off_value
, or dtype
are provided, dtype
will default to the
value tf.float32
Examples
Suppose that
indices = [0, 2, 1, 1]
depth = 3
on_value = 5.0
off_value = 0.0
axis = 1
Then output is [4 x 3]
:
output =
[5.0 0.0 0.0] // one_hot(0)
[0.0 0.0 5.0] // one_hot(2)
[0.0 0.0 0.0] // one_hot(1)
[0.0 5.0 0.0] // one_hot(1)
Suppose that
indices = [[0, 2], [1, 1]]
depth = 3
on_value = 1.0
off_value = 0.0
axis = 1
Then output is [2 x 2 x 3]
:
output =
[
[1.0, 0.0, 0.0] // one_hot(0)
[0.0, 0.0, 1.0] // one_hot(2)
][
[0.0, 1.0, 0.0] // one_hot(1)
[0.0, 0.0, 0.0] // one_hot(1)
]
Using default values for on_value
and off_value
:
indices = [0, 1, 2]
depth = 3
The output will be
output =
[[1., 0., 0.],
[0., 1., 0.],
[0., 0., 1.]]
Args:
indices
: ATensor
of indices.depth
: A scalar defining the depth of the one hot dimension.on_value
: A scalar defining the value to fill in output whenindices[j] = i
. (default: 1)off_value
: A scalar defining the value to fill in output whenindices[j] != i
. (default: 0)axis
: The axis to fill (default: 1, a new innermost axis).dtype
: The data type of the output tensor.
Returns:
output
: The onehot tensor.
Raises:
TypeError
: If dtype of eitheron_value
oroff_value
don't matchdtype
TypeError
: If dtype ofon_value
andoff_value
don't match one another