xview — xtensor documentation (original) (raw)
Defined in xtensor/views/xview.hpp
template<class CT, class ...S>
class xview : public xt::xview_semantic<xview<CT, S...>>, public std::conditional_t<detail::is_contiguous_view<std::decay_t<CT>, S...>::value, xcontiguous_iterable<xview<CT, S...>>, xiterable<xview<CT, S...>>>, public xt::xaccessible<xview<CT, S...>>, public extension::xview_base_t<CT, S...>
Multidimensional view with tensor semantic.
The xview class implements a multidimensional view with tensor semantic. It is used to adapt the shape of an xexpression without changing it. xview is not meant to be used directly, but only with the view helper functions.
Template Parameters:
- CT – the closure type of the xexpression to adapt
- S – the slices type describing the shape adaptation
Constructor
template<class CTA, class FSL, class ...SL>
explicit xview(CTA &&e, FSL &&first_slice, SL&&... slices) noexcept
Constructs a view on the specified xexpression.
Users should not call directly this constructor but use the view function instead.
Parameters:
- e – the xexpression to adapt
- first_slice – the first slice describing the view
- slices – the slices list describing the view
Size and shape
inline const inner_shape_type &shape() const noexcept
Returns the shape of the view.
inline const slice_type &slices() const noexcept
Returns the slices of the view.
inline layout_type layout() const noexcept
Returns the slices of the view.
Data
template<class T>
inline void fill(const T &value)
Fills the view with the given value.
Parameters:
value – the value to fill the view with.
inline xexpression_type &expression() noexcept
Returns a reference to the underlying expression of the view.
inline const xexpression_type &expression() const noexcept
Returns a const reference to the underlying expression of the view.
template<class T = xexpression_type> inline std::size_t data_offset () const noexcept requires(has_data_interface_concept< T > and strided_view_concept< CT
Return the offset to the first element of the view in the underlying container.
template<class ...Args>
inline auto operator()(Args... args) -> reference
Returns a reference to the element at the specified position in the view.
Parameters:
args – a list of indices specifying the position in the view. Indices must be unsigned integers, the number of indices should be equal or greater than the number of dimensions of the view.
template<class ...Args>
inline auto unchecked(Args... args) -> reference
Returns a reference to the element at the specified position in the view.
Warning
This method is meant for performance, for expressions with a dynamic number of dimensions (i.e. not known at compile time). Since it may have undefined behavior (see parameters), operator() should be preferred whenever it is possible.
Warning
This method is NOT compatible with broadcasting, meaning the following code has undefined behavior:
xt::xarray a = {{0, 1}, {2, 3}}; xt::xarray b = {0, 1}; auto fd = a + b; double res = fd.unchecked(0, 1);
Parameters:
args – a list of indices specifying the position in the view. Indices must be unsigned integers, the number of indices must be equal to the number of dimensions of the view, else the behavior is undefined.
template<class ...Args>
inline auto operator()(Args... args) const -> const_reference
Returns a constant reference to the element at the specified position in the view.
Parameters:
args – a list of indices specifying the position in the view. Indices must be unsigned integers, the number of indices should be equal or greater than the number of dimensions of the view.
template<class ...Args>
inline auto unchecked(Args... args) const -> const_reference
Returns a constant reference to the element at the specified position in the view.
Warning
This method is meant for performance, for expressions with a dynamic number of dimensions (i.e. not known at compile time). Since it may have undefined behavior (see parameters), operator() should be preferred whenever it is possible.
Warning
This method is NOT compatible with broadcasting, meaning the following code has undefined behavior:
xt::xarray a = {{0, 1}, {2, 3}}; xt::xarray b = {0, 1}; auto fd = a + b; double res = fd.unchecked(0, 1);
Parameters:
args – a list of indices specifying the position in the view. Indices must be unsigned integers, the number of indices must be equal to the number of dimensions of the view, else the behavior is undefined.
template<class T>
inline auto storage() -> storage_type&
requires (has_data_interface_concept<T>)
Returns the data holder of the underlying container (only if the view is on a realized container).
[xt::eval](xeval.html#group%5F%5Fxt%5F%5Fxeval%5F1gafb957ae0ad1b7f97b9bf4d977ae24a86) will make sure that the underlying xexpression is on a realized container.
template<class T>
inline auto strides() const -> const inner_strides_type&
requires (has_data_interface_concept<T> and strided_view_concept<CT, S...>)
Return the strides for the underlying container of the view.
template<class T>
inline auto data() const -> const_pointer
requires (has_data_interface_concept<T> and strided_view_concept<CT, S...>)
Return the pointer to the underlying buffer.
Broadcasting
template<class ST>
inline bool broadcast_shape(ST &shape, bool reuse_cache = false) const
Broadcast the shape of the view to the specified parameter.
Parameters:
- shape – the result shape
- reuse_cache – parameter for internal optimization
Returns:
a boolean indicating whether the broadcasting is trivial
template<class ST>
inline bool has_linear_assign(const ST &strides) const
Checks whether the xview can be linearly assigned to an expression with the specified strides.
Returns:
a boolean indicating whether a linear assign is possible
Extended copy semantic
template<class E>
inline auto operator=(const xexpression<E> &e) -> self_type&
The extended assignment operator.
template<class E, class ...S>
inline auto xt::view(E &&e, S&&... slices)
Constructs and returns a view on the specified xexpression.
Users should not directly construct the slices but call helper functions instead.
Parameters:
- e – the xexpression to adapt
- slices – the slices list describing the view.
viewaccepts negative indices, in that case indexing is done in reverse order.
template<class E>
inline auto xt::row(E &&e, std::ptrdiff_t index)
Constructs and returns a row (sliced view) on the specified expression.
Users should not directly construct the slices but call helper functions instead. This function is only allowed on expressions with two dimensions.
Parameters:
- e – the xexpression to adapt
- index – 0-based index of the row, negative indices will return the last rows in reverse order.
Throws:
std::invalid_argument – if the expression has more than 2 dimensions.
template<class E>
inline auto xt::col(E &&e, std::ptrdiff_t index)
Constructs and returns a column (sliced view) on the specified expression.
Users should not directly construct the slices but call helper functions instead. This function is only allowed on expressions with two dimensions.
Parameters:
- e – the xexpression to adapt
- index – 0-based index of the column, negative indices will return the last columns in reverse order.
Throws:
std::invalid_argument – if the expression has more than 2 dimensions.
Defined in xtensor/views/xslice.hpp
template<class A, class B>
inline auto xt::range(A start_val, B stop_val)
Select a range from start_val to stop_val (excluded).
You can use the shorthand _ syntax to select from the start or until the end.
using namespace xt::placeholders; // to enable _ syntax
range(3, ) // select from index 3 to the end
range(, 5) // select from index 0 to 5 (excluded)
range(_, _) // equivalent to all()
template<class A, class B, class C>
inline auto xt::range(A start_val, B stop_val, C step)
Select a range from start_val to stop_val (excluded) with step You can use the shorthand _ syntax to select from the start or until the end.
using namespace xt::placeholders; // to enable _ syntax range(3, _, 5) // select from index 3 to the end with stepsize 5
Warning
doxygenfunction: Unable to resolve function “xt::all” with arguments None in doxygen xml output for project “xtensor” from directory: ../xml. Potential matches:
- auto all() noexcept
- template bool all(E &&e)
inline auto xt::newaxis() noexcept
Returns a slice representing a new axis of length one, to be used as an argument of view function.
inline auto xt::ellipsis() noexcept
Returns a slice representing all remaining dimensions, and selecting all in these dimensions.
Ellipsis will expand to a series of [all()](operators.html#group%5F%5Flogical%5F%5Foperators%5F1ga8da84f179efb13f3d860c5950b5c626e) slices, until the number of slices is equal to the number of dimensions of the source array.
Note: ellipsis can only be used in strided_view!
xarray a = xarray::from_shape({5, 5, 1, 1, 5}); auto v = xt::strided_view(a, {2, xt::ellipsis(), 2}); // equivalent to using {2, xt::all(), xt::all(), xt::all(), 2};
template<class R = std::ptrdiff_t, class T>
inline auto xt::keep(T &&indices)
Create a non-contigous slice from a container of indices to keep.
Note: this slice cannot be used in the xstrided_view!
xt::xarray a = xt::arange(9); a.reshape({3, 3}); xt::view(a, xt::keep(0, 2); // => {{0, 1, 2}, {6, 7, 8}} xt::view(a, xt::keep(1, 1, 1); // => {{3, 4, 5}, {3, 4, 5}, {3, 4, 5}}
Parameters:
indices – The indices container
Returns:
instance of xkeep_slice
template<class R = std::ptrdiff_t, class T>
inline auto xt::drop(T &&indices)
Create a non-contigous slice from a container of indices to drop.
Note: this slice cannot be used in the xstrided_view!
xt::xarray a = xt::arange(9); a.reshape({3, 3}); xt::view(a, xt::drop(0, 2); // => {{3, 4, 5}}
Parameters:
indices – The container of indices to drop
Returns:
instance of xdrop_slice