xindexview¶
Defined in xtensor/xindexview.hpp
- template <class CT, class I>
-
class
xt::
xindexview
¶ View of an xexpression from vector of indices.
The xindexview class implements a flat (1D) view into a multidimensional xexpression yielding the values at the indices of the index array. xindexview is not meant to be used directly, but only with the index_view and filter helper functions.
- See
- index_view, filter
- Template Parameters
CT
: the closure type of the xexpression type underlying this viewI
: the index array type of the view
Inherits from xt::xview_semantic< xindexview< CT, I > >, xt::xexpression_iterable< xindexview< CT, I > >
Extended copy semantic
- template <class E>
-
auto
operator=
(const xexpression<E> &e)¶ The extended assignment operator.
Constructor
- template <class I2>
-
xindexview
(CT e, I2 &&indices)¶ Constructs an xindexview, selecting the indices specified by indices.
The resulting xexpression has a 1D shape with a length of n for n indices.
- Parameters
e
: the underlying xexpression for this viewindices
: the indices to select
Size and shape
-
auto
size
() const¶ Returns the size of the xindexview.
-
auto
dimension
() const¶ Returns the number of dimensions of the xindexview.
-
auto
shape
() const¶ Returns the shape of the xindexview.
Data
- template <class... Args>
-
auto
operator()
(std::size_t idx, Args...) const¶ Returns the element at the specified position in the xindexview.
- Parameters
idx
: the position in the view
- template <class It>
-
auto
element
(It first, It)¶ Returns a reference to the element at the specified position in the xindexview.
- Parameters
first
: iterator starting the sequence of indices The number of indices in the sequence should be equal to or greater 1.
Broadcasting
- template <class O>
-
bool
broadcast_shape
(O &shape) const¶ Broadcast the shape of the xindexview to the specified parameter.
- Return
- a boolean indicating whether the broadcasting is trivial
- Parameters
shape
: the result shape
- template <class O>
-
bool
is_trivial_broadcast
(const O&) const¶ Compares the specified strides with those of the container to see whether the broadcasting is trivial.
- Return
- a boolean indicating whether the broadcasting is trivial
- template <class ECT, class CCT>
-
class
xt::
xfiltration
¶ Filter of a xexpression for fast scalar assign.
The xfiltration class implements a lazy filtration of a multidimentional xexpression, optimized for scalar and computed scalar assignments. Actually, the xfiltration class IS NOT an xexpression and the scalar and computed scalar assignments are the only method it provides. The filtering condition is not evaluated until the filtration is assigned.
xfiltration is not meant to be used directly, but only with the filtration helper function.
- See
- filtration
- Template Parameters
ECT
: the closure type of the xexpression type underlying this filtrationCCR
: the closure type of the filtering xexpression type
Extended copy semantic
- template <class E>
-
auto
operator=
(const E &e)¶ Assigns the scalar
e
to*this
.- Return
- a reference to \ *this.
- Parameters
e
: the scalar to assign.
Constructor
-
xfiltration
(ECT e, CCT condition)¶ Constructs a xfiltration on the given expression
e
, selecting the elements matching the specifiedcondition
.- Parameters
e
: the xexpression to filter.condition
: the filtering xexpression to apply.
Computed assignement
- template <class E>
-
auto
operator+=
(const E &e)¶ Adds the scalar
e
to*this
.- Return
- a reference to
*this
. - Parameters
e
: the scalar to add.
- template <class E>
-
auto
operator-=
(const E &e)¶ Subtracts the scalar
e
from*this
.- Return
- a reference to
*this
. - Parameters
e
: the scalar to subtract.
- template <class E>
-
auto
operator*=
(const E &e)¶ Multiplies
*this
with the scalare
.- Return
- a reference to
*this
. - Parameters
e
: the scalar involved in the operation.
- template <class E>
-
auto
operator/=
(const E &e)¶ Divides
*this
by the scalare
.- Return
- a reference to
*this
. - Parameters
e
: the scalar involved in the operation.
- template <class E, class I>
-
auto
xt::
index_view
(E &&e, I &&indices)¶ creates an indexview from a container of indices.
Returns a 1D view with the elements at indices selected.
xarray<double> a = {{1,5,3}, {4,5,6}}; b = index_view(a, {{0, 0}, {1, 0}, {1, 1}}); std::cout << b << std::endl; // {1, 4, 5} b += 100; std::cout << a << std::endl; // {{101, 5, 3}, {104, 105, 6}}
- Parameters
e
: the underlying xexpressionindices
: the indices to select
- template <class E, class O>
-
auto
xt::
filter
(E &&e, O &&condition)¶ creates a view into e filtered by condition.
Returns a 1D view with the elements selected where condition evaluates to true. This is equivalent to
The returned view is not optimal if you just want to assign a scalar to the filtered elements. In that case, you should consider using the filtration function instead.{index_view(e, where(condition));}
xarray<double> a = {{1,5,3}, {4,5,6}}; b = filter(a, a >= 5); std::cout << b << std::endl; // {5, 5, 6}
- Parameters
e
: the underlying xexpressioncondition
: xexpression with shape of e which selects indices
- See
- filtration
- template <class E, class C>
-
auto
xt::
filtration
(E &&e, C &&condition)¶ creates a filtration of
e
filtered by condition.Returns a lazy filtration optimized for scalar assignment. Actually, scalar assignment and computed scalar assignments are the only available methods of the filtration, the filtration IS NOT an xexpression.
xarray<double> a = {{1,5,3}, {4,5,6}}; filtration(a, a >= 5) += 2; std::cout << a << std::endl; // {{1, 7, 3}, {4, 7, 8}}
- Parameters
e
: the xexpression to filtercondition
: the filtering xexpression