std::ranges:: views::chunk_by, std::ranges::

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< cpp‎ | ranges
C++
Ranges library
Range adaptors
(C++23)(C++23)
(C++23)
(C++23)(C++23)
(C++23)
(C++23)(C++23)
(C++23)(C++23)
chunk_by_viewviews::chunk_by
(C++23)(C++23)
(C++23)(C++23)
(C++23)(C++23)

std::ranges::chunk_by_view
Defined in header <ranges>
template < ranges::forward_range V, std::indirect_binary_predicate <iterator_t<V>,

ranges::iterator_t <V>> Pred >
    requires ranges::view <V> && std::is_object_v <Pred>
class chunk_by_view

: public ranges::view_interface <chunk_by_view<V, Pred>>
(1) (since C++23)
namespace views {

inline constexpr /* unspecified */ chunk_by = /* unspecified */ ;

}
(2) (since C++23)
Call signature
template < ranges::viewable_range R, class Pred >

requires /* see below */

constexpr ranges::view auto chunk_by( R&& r, Pred&& pred ) ;
(since C++23)
template < class Pred >
constexpr /*range adaptor closure*/ chunk_by( Pred&& pred ) ;
(since C++23)
1) chunk_by_view is a range adaptor that takes a view and an invocable object pred (the binary predicate), and produces a view of subranges (chunks), by splitting the underlying view between each pair of adjacent elements for which pred returns false
2) The name views::chunk_by denotes a RangeAdaptorObject. Given a subexpression e and f, the expression views::chunk_by(e, f) is expression-equivalent to chunk_by_view(e, f)

chunk_by_view always models forward_range, and models bidirectional_range and/or common_range, if adapted view type models the corresponding concepts. chunk_by_view never models borrowed_range or sized_range

Data members

Member Definition
V base_ the underlying view
(exposition-only member object*
movable-box<Pred> pred_ an object that wraps the predicate used to split the elements of base_
(exposition-only member object*
non-propagating-cache<iterator> begin_ an object that caches the iterator to the first element
(exposition-only member object*

Member functions

 constructs a chunk_by_view
(public member function)
returns a copy of the underlying (adapted) view
(public member function)
returns a reference to the stored predicate
(public member function)
returns an iterator to the beginning
(public member function)
returns an iterator or a sentinel to the end
(public member function)
returns an iterator to the begin of the next subrange
(exposition-only member function*
returns an iterator to the begin of the previous subrange
(exposition-only member function*
Inherited from std::ranges::view_interface
returns whether the derived view is empty. Provided if it satisfies sized_range or forward_range.
(public member function of std::ranges::view_interface<D>)
(C++23)
 returns a constant iterator to the beginning of the range.
(public member function of std::ranges::view_interface<D>)
(C++23)
 returns a sentinel for the constant iterator of the range.
(public member function of std::ranges::view_interface<D>)
returns whether the derived view is not empty. Provided if ranges::empty is applicable to it.
(public member function of std::ranges::view_interface<D>)
returns the first element in the derived view. Provided if it satisfies forward_range.
(public member function of std::ranges::view_interface<D>)
returns the last element in the derived view. Provided if it satisfies bidirectional_range and common_range.
(public member function of std::ranges::view_interface<D>)

Deduction guides

Nested classes

 the iterator type
(exposition-only member class template*

Notes

In order to provide the amortized constant time complexity required by the range concept, the result of begin() is cached within the chunk_by_view object. If the underlying range is modified after the first call to begin(), subsequent uses of the chunk_by_view

Feature-test macro Value Std Feature
__cpp_lib_ranges_chunk_by 202202L (C++23) std::ranges::chunk_by_view

Example

Run this code
#include <functional>
#include <iostream>
#include <ranges>
#include <string_view>
 
void print_chunks(auto view, std::string_view separator = ", ")
{
    for (auto const subrange : view)
    {
        std::cout << '[';
        for (std::string_view prefix; auto const& elem : subrange)
            std::cout << prefix << elem, prefix = separator;
        std::cout << "] ";
    }
    std::cout << '\n';
}
 
int main()
{
    std::initializer_list v1 = {1, 2, 3, 1, 2, 3, 3, 3, 1, 2, 3};
    auto fn1 = std::ranges::less{};
    auto view1 = v1 | std::views::chunk_by(fn1);
    print_chunks(view1);
 
    std::initializer_list v2 = {1, 2, 3, 4, 4, 0, 2, 3, 3, 3, 2, 1};
    auto fn2 = std::ranges::not_equal_to{};
    auto view2 = v2 | std::views::chunk_by(fn2);
    print_chunks(view2);
 
    std::string_view v3 = "__cpp_lib_ranges_chunk_by";
    auto fn3 = [](auto x, auto y) { return not(x == '_' or y == '_'); };
    auto view3 = v3 | std::views::chunk_by(fn3);
    print_chunks(view3, "");
 
    std::string_view v4 = "\u007a\u00df\u6c34\u{1f34c}"; // "zß水🍌"
    auto fn4 = [](auto, auto ß) { return 128 == ((128 + 64) & ß); };
    auto view4 = v4 | std::views::chunk_by(fn4);
    print_chunks(view4, "");
}

Output: 

[1, 2, 3] [1, 2, 3] [3] [3] [1, 2, 3] 
[1, 2, 3, 4] [4, 0, 2, 3] [3] [3, 2, 1] 
[_] [_] [cpp] [_] [lib] [_] [ranges] [_] [chunk] [_] [by]
[z] [ß] [水] [🍌]

References

  • C++23 standard (ISO/IEC 14882:2024):
  • 26.7.30 Chunk by view [range.chunk.by]

See also

(C++23)
 a range of views that are N-sized non-overlapping successive chunks of the elements of another view
(class template) (range adaptor object)
(C++23)
 a view whose Mth element is a view over the Mth through (M + N - 1)th elements of another view
(class template) (range adaptor object)
(C++23)
 a view consisting of elements of another view, advancing over N elements at a time
(class template) (range adaptor object)
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