Return a strided slice from
Note, most python users will want to use the Python
Variable.__getitem__ rather than this op directly.
The goal of this op is to produce a new tensor with a subset of the elements from the
input tensor. The subset is chosen using a sequence of
m sparse range specifications encoded into the arguments of this function. Note, in some cases
m could be equal to
n, but this need not be the case. Each range specification entry can be one of the following:
- An ellipsis (...). Ellipses are used to imply zero or more dimensions of full-dimension selection and are produced using
ellipsis_mask. For example,
foo[...]is the identity slice.
- A new axis. This is used to insert a new shape=1 dimension and is produced using
new_axis_mask. For example,
(3, 4)produces a
(1, 3, 4)tensor.
- A range
begin:end:stride. This is used to specify how much to choose from a given dimension.
stridecan be any integer but 0.
beginis an integer which represents the index of the first value to select while
endrepresents the index of the last value to select. The number of values selected in each dimension is
end - beginif
stride > 0and
begin - endif
stride < 0.
endcan be negative where
-1is the last element,
-2is the second to last.
begin_maskcontrols whether to replace the explicitly given
beginwith an implicit effective value of
stride > 0and
stride < 0.
end_maskis analogous but produces the number required to create the largest open interval. For example, given a shape
foo[:], the effective
3. Do not assume this is equivalent to
foo[0:-1]which has an effective
2. Another example is
foo[-2::-1]which reverses the first dimension of a tensor while dropping the last two (in the original order elements). For example
foo = [1,2,3,4]; foo[-2::-1]is
- A single index. This is used to keep only elements that have a given index. For example (
foo[2, :]on a shape
(5,6)tensor produces a shape
(6,)tensor. This is encoded in
Each conceptual range specification is encoded in the op's argument. This encoding is best understand by considering a non-trivial example. In particular,
foo[1, 2:4, None, ..., :-3:-1, :] will be encoded as
``` begin = [1, 2, x, x, 0, x] # x denotes don't care (usually 0) end = [2, 4, x, x, -3, x] strides = [1, 1, x, x, -1, 1] begin_mask = 1<<4 | 1 << 5 = 48 end_mask = 1<<5 = 32 ellipsis_mask = 1<<3 = 8 new_axis_mask = 1<<2 4 shrink_axis_mask = 1<<0 ```
In this case if `foo.shape` is (5, 5, 5, 5, 5, 5) the final shape of the slice becomes (2, 1, 5, 5, 2, 5). Let us walk step by step through each argument specification.
- The first argument in the example slice is turned into `begin = 1` and `end = begin + 1 = 2`. To disambiguate from the original spec `2:4` we also set the appropriate bit in `shrink_axis_mask`.
- `2:4` is contributes 2, 4, 1 to begin, end, and stride. All masks have zero bits contributed.
- None is a synonym for `tf.newaxis`. This means insert a dimension of size 1 dimension in the final shape. Dummy values are contributed to begin, end and stride, while the new_axis_mask bit is set.
- `...` grab the full ranges from as many dimensions as needed to fully specify a slice for every dimension of the input shape.
- `:-3:-1` shows the use of negative indices. A negative index `i` associated with a dimension that has shape `s` is converted to a positive index `s + i`. So `-1` becomes `s-1` (i.e. the last element). This conversion is done internally so begin, end and strides receive x, -3, and -1. The appropriate begin_mask bit is set to indicate the start range is the full range (ignoring the x).
- `:` indicates that the entire contents of the corresponding dimension is selected. This is equivalent to `::` or `0::1`. begin, end, and strides receive 0, 0, and 1, respectively. The appropriate bits in `begin_mask` and `end_mask` are also set.
*Requirements*: `0 != strides[i] for i in [0, m)` `ellipsis_mask must be a power of two (only one ellipsis)`
- scope: A Scope object
- begin: `begin[k]` specifies the offset into the `k`th range specification. The exact dimension this corresponds to will be determined by context. Out-of-bounds values will be silently clamped. If the `k`th bit of `begin_mask` then `begin[k]` is ignored and the full range of the appropriate dimension is used instead. Negative values causes indexing to start from the highest element e.g. If `foo==[1,2,3]` then `foo[-1]==3`.
- end: `end[i]` is like `begin` with the exception that `end_mask` is used to determine full ranges.
- strides: `strides[i]` specifies the increment in the `i`th specification after extracting a given element. Negative indices will reverse the original order. Out or range values are clamped to `[0,dim[i]) if slice[i]>0
or[-1,dim[i]-1] if slice[i] < 0`
Optional attributes (see
- begin_mask: a bitmask where a bit i being 1 means to ignore the begin value and instead use the largest interval possible. At runtime begin[i] will be replaced with
[0, n-1) ifstride[i] > 0
ifstride[i] < 0
end_mask: analogous tobegin_mask
ellipsis_mask: a bitmask where biti
being 1 means thei`th position is actually an ellipsis. One bit at most can be 1. If
ellipsis_mask == 0, then an implicit ellipsis mask of
1 << (m+1)is provided. This means that
foo[3:5] == foo[3:5, ...]. An ellipsis implicitly creates as many range specifications as necessary to fully specify the sliced range for every dimension. For example for a 4-dimensional tensor
foo[2, ..., 5:8]implies
foo[2, :, :, 5:8].
- new_axis_mask: a bitmask where bit
ibeing 1 means the
ith specification creates a new shape 1 dimension. For example
foo[:4, tf.newaxis, :2]would produce a shape
(4, 1, 2)tensor.
- shrink_axis_mask: a bitmask where bit
iimplies that the
ith specification should shrink the dimensionality. begin and end must imply a slice of size 1 in the dimension. For example in python one might do
foo[:, 3, :]which would result in
Output: The output tensor.
Constructors and Destructors
Public static functions
Optional attribute setters for StridedSlice.
StridedSlice( const ::tensorflow::Scope & scope, ::tensorflow::Input input, ::tensorflow::Input begin, ::tensorflow::Input end, ::tensorflow::Input strides )
StridedSlice( const ::tensorflow::Scope & scope, ::tensorflow::Input input, ::tensorflow::Input begin, ::tensorflow::Input end, ::tensorflow::Input strides, const StridedSlice::Attrs & attrs )
::tensorflow::Node * node() const
Public static functions
Attrs BeginMask( int64 x )
Attrs EllipsisMask( int64 x )
Attrs EndMask( int64 x )
Attrs NewAxisMask( int64 x )
Attrs ShrinkAxisMask( int64 x )