xstrided_view

Defined in xtensor/views/xstrided_view.hpp

template<class CT, class S, layout_type L = layout_type::dynamic, class FST = detail::flat_storage_getter<CT, ::xt::layout_type::row_major>>
class xstrided_view : public xt::xview_semantic<xstrided_view<CT, S, layout_type::dynamic, detail::flat_storage_getter<CT, ::xt::layout_type::row_major>>>, public select_iterable_base_t<layout_type::dynamic, std::decay_t<CT>::static_layout, xstrided_view<CT, S, layout_type::dynamic, detail::flat_storage_getter<CT, ::xt::layout_type::row_major>>>, private xt::xstrided_view_base<xstrided_view<CT, S, layout_type::dynamic, detail::flat_storage_getter<CT, ::xt::layout_type::row_major>>>, public extension::xstrided_view_base_t<CT, S, layout_type::dynamic, detail::flat_storage_getter<CT, ::xt::layout_type::row_major>>

View of an xexpression using strides.

The xstrided_view class implements a view utilizing an initial offset and strides.

See also

strided_view, transpose

Template Parameters:

  • CT – the closure type of the xexpression type underlying this view

  • L – the layout of the strided view

  • S – the strides type of the strided view

  • FST – the flat storage type used for the strided view

Constructor

template<class CTA, class SA>
inline xstrided_view(CTA &&e, SA &&shape, strides_type &&strides, std::size_t offset, layout_type layout) noexcept

Constructs an xstrided_view.

Parameters:

  • e – the underlying xexpression for this view

  • shape – the shape of the view

  • strides – the strides of the view

  • offset – the offset of the first element in the underlying container

  • layout – the layout of the view

Extended copy semantic

template<class E>
inline self_type &operator=(const xexpression<E> &e)

The extended assignment operator.

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.

Public Functions

const inner_backstrides_type &backstrides() const noexcept

Returns the backstrides of the xtrided_view_base.

layout_type layout() const noexcept

Returns the layout of the xtrided_view_base.

const inner_shape_type &shape() const noexcept

Returns the shape of the xtrided_view_base.

const inner_strides_type &strides() const noexcept

Returns the strides of the xtrided_view_base.

reference operator()(Args... args)

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.

const_reference operator()(Args... args) const

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.

reference unchecked(Args... args)

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<double> a = {{0, 1}, {2, 3}};
xt::xarray<double> b = {0, 1};
auto fd = a + b;
double res = fd.uncheked(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.

const_reference unchecked(Args... args) const

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<double> a = {{0, 1}, {2, 3}};
xt::xarray<double> b = {0, 1};
auto fd = a + b;
double res = fd.uncheked(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.

pointer data() noexcept

Returns a pointer to the underlying array serving as element storage.

The first element of the view is at data() + data_offset().

const_pointer data() const noexcept

Returns a constant pointer to the underlying array serving as element storage.

The first element of the view is at data() + data_offset().

size_type data_offset() const noexcept

Returns the offset to the first element in the view.

reference element(It first, It last)

Returns a reference to the element at the specified position in the view.

Parameters:

  • first – iterator starting the sequence of indices

  • last – iterator ending the sequence of indices The number of indices in the sequence should be equal to or greater than the the number of dimensions of the view..

const_reference element(It first, It last) const

Returns a constant reference to the element at the specified position in the view.

Parameters:

  • first – iterator starting the sequence of indices

  • last – iterator ending the sequence of indices The number of indices in the sequence should be equal to or greater than the the number of dimensions of the view..

xexpression_type &expression() noexcept

Returns a reference to the underlying expression of the view.

const xexpression_type &expression() const noexcept

Returns a constant reference to the underlying expression of the view.

storage_type &storage() noexcept

Returns a reference to the buffer containing the elements of the view.

const storage_type &storage() const noexcept

Returns a constant reference to the buffer containing the elements of the view.

bool broadcast_shape(O &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

bool has_linear_assign(const O &strides) const noexcept

Checks whether the xstrided_view_base can be linearly assigned to an expression with the specified strides.

Returns:

a boolean indicating whether a linear assign is possible

using xt::xstrided_slice_vector = std::vector<xstrided_slice<std::ptrdiff_t>>

vector of slices used to build a xstrided_view

template<layout_type L = layout_type::dynamic, class E, class S, class X>
inline auto xt::strided_view(E &&e, S &&shape, X &&strides, std::size_t offset, layout_type layout) noexcept

Construct a strided view from an xexpression, shape, strides and offset.

Parameters:

  • e – xexpression

  • shape – the shape of the view

  • strides – the new strides of the view

  • offset – the offset of the first element in the underlying container

  • layout – the new layout of the expression

Template Parameters:

  • L – the static layout type of the view (default: dynamic)

  • E – type of xexpression

  • S – strides type

  • X – strides type

Returns:

the view

template<class E>
inline auto xt::strided_view(E &&e, const xstrided_slice_vector &slices)

Function to create a dynamic view from an xexpression and an xstrided_slice_vector. 

xt::xarray<double> a = {{1, 2, 3}, {4, 5, 6}};
xt::xstrided_slice_vector sv({xt::range(0, 1)});
sv.push_back(xt::range(0, 3, 2));
auto v = xt::strided_view(a, sv);
// ==> {{1, 3}}

You can also achieve the same with the following short-hand syntax:

xt::xarray<double> a = {{1, 2, 3}, {4, 5, 6}};
auto v = xt::strided_view(a, {xt::range(0, 1), xt::range(0, 3, 2)});
// ==> {{1, 3}}
Parameters:

  • e – xexpression

  • slices – the slice vector

Returns:

initialized strided_view according to slices

template<layout_type L = ::xt::layout_type::row_major, class E, class S>
inline auto xt::reshape_view(E &&e, S &&shape, layout_type)

Return a view on a container with a new shape.

Deprecated:

Note: if you resize the underlying container, this view becomes invalidated.

Parameters:

  • e – xexpression to reshape

  • shape – new shape

  • order – traversal order (optional)

Returns:

view on xexpression with new shape