# layout¶

Defined in xtensor/xlayout.hpp

enum xt::layout_type

layout_type enum for xcontainer based xexpressions

Values:

dynamic = 0x00

dynamic layout_type: you can resize to row major, column major, or use custom strides

any = 0xFF

layout_type compatible with all others

row_major = 0x01

row major layout_type

column_major = 0x02

column major layout_type

template<class ...Args>
constexpr layout_type xt::compute_layout(Args... args)

Implementation of the following logical table:

  | d | a | r | c |
--+---+---+---+---+
d | d | d | d | d |
a | d | a | r | c |
r | d | r | r | d |
c | d | c | d | c |
d = dynamic, a = any, r = row_major, c = column_major.

Using bitmasks to avoid nested if-else statements.

Return

the output layout, computed with the previous logical table.

Parameters
• args: the input layouts.

# xcontainer¶

Defined in xtensor/xcontainer.hpp

template<class D>
class xcontainer : public xt::xcontiguous_iterable<D>, private xt::xaccessible<D>

Base class for dense multidimensional containers.

The xcontainer class defines the interface for dense multidimensional container classes. It does not embed any data container, this responsibility is delegated to the inheriting classes.

Template Parameters
• D: The derived type, i.e. the inheriting class for which xcontainer provides the interface.

Subclassed by xt::xstrided_container< D >

Size and shape

auto size() const

Returns the number of element in the container.

constexpr auto dimension() const

Returns the number of dimensions of the container.

constexpr auto shape() const

Returns the shape of the container.

constexpr auto strides() const

Returns the strides of the container.

constexpr auto backstrides() const

Returns the backstrides of the container.

Data

template<class T>
void fill(const T &value)

Fills the container with the given value.

Parameters
• value: the value to fill the container with.

auto storage()

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

auto storage() const

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

auto data()

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

The pointer is such that range [data(); data() + size()] is always a valid range, even if the container is empty (data() is not is not dereferenceable in that case)

auto data() const

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

The pointer is such that range [data(); data() + size()] is always a valid range, even if the container is empty (data() is not is not dereferenceable in that case)

auto data_offset() const

Returns the offset to the first element in the container.

template<class ...Args>
auto operator()(Args... args)

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

Parameters
• args: a list of indices specifying the position in the container. Indices must be unsigned integers, the number of indices should be equal or greater than the number of dimensions of the container.

template<class ...Args>
auto operator()(Args... args) const

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

Parameters
• args: a list of indices specifying the position in the container. Indices must be unsigned integers, the number of indices should be equal or greater than the number of dimensions of the container.

template<class ...Args>
auto unchecked(Args... args)

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

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 prefered 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 container. Indices must be unsigned integers, the number of indices must be equal to the number of dimensions of the container, else the behavior is undefined.

template<class ...Args>
auto unchecked(Args... args) const

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

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 prefered 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 container. Indices must be unsigned integers, the number of indices must be equal to the number of dimensions of the container, else the behavior is undefined.

template<class It>
auto element(It first, It last)

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

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 number of dimensions of the container.

template<class It>
auto element(It first, It last) const

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

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 number of dimensions of the container.

template<class S>
bool broadcast_shape(S &shape, bool reuse_cache = false) const

Broadcast the shape of the container to the specified parameter.

Return

a boolean indicating whether the broadcasting is trivial

Parameters
• shape: the result shape

• reuse_cache: parameter for internal optimization

template<class S>
bool has_linear_assign(const S &strides) const

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

Return

a boolean indicating whether a linear assign is possible

# xstrided_container¶

Defined in xtensor/xcontainer.hpp

template<class D>
class xstrided_container : public xt::xcontainer<D>

Partial implementation of xcontainer that embeds the strides and the shape.

The xstrided_container class is a partial implementation of the xcontainer interface that embed the strides and the shape of the multidimensional container. It does not embed the data container, this responsibility is delegated to the inheriting classes.

Template Parameters
• D: The derived type, i.e. the inheriting class for which xstrided_container provides the partial imlpementation of xcontainer.

Subclassed by xt::xarray_container< value_type >

Public Functions

template<class S = shape_type>
void resize(S &&shape, bool force = false)

Resizes the container.

Warning

Contrary to STL containers like std::vector, resize does NOT preserve the container elements.

Parameters
• shape: the new shape

• force: force reshaping, even if the shape stays the same (default: false)

template<class S = shape_type>
void resize(S &&shape, layout_type l)

Resizes the container.

Warning

Contrary to STL containers like std::vector, resize does NOT preserve the container elements.

Parameters
• shape: the new shape

• l: the new layout_type

template<class S = shape_type>
void resize(S &&shape, const strides_type &strides)

Resizes the container.

Warning

Contrary to STL containers like std::vector, resize does NOT preserve the container elements.

Parameters
• shape: the new shape

• strides: the new strides

layout_type layout() const

Return the layout_type of the container.

Return

layout_type of the container

template<class S>
auto &reshape(S &&shape, layout_type layout) &

Reshapes the container and keeps old elements.

The shape argument can have one of its value equal to -1, in this case the value is inferred from the number of elements in the container and the remaining values in the shape.

xt::xarray<int> a = { 1, 2, 3, 4, 5, 6, 7, 8 };
a.reshape({-1, 4});
//a.shape() is {2, 4}

Parameters
• shape: the new shape (has to have same number of elements as the original container)

• layout: the layout to compute the strides (defaults to static layout of the container, or for a container with dynamic layout to XTENSOR_DEFAULT_LAYOUT)