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

 

C++

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Standard library

Standard library headers

Named requirements

Feature test macros (C++20)

Language support library

Concepts library (C++20)

Metaprogramming library (C++11)

Diagnostics library

General utilities library

Strings library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Numerics library

Localizations library

Input/output library

Filesystem library (C++17)

Regular expressions library (C++11)

Concurrency support library (C++11)

Execution support library (C++26)

Technical specifications

Symbols index

External libraries

 

Ranges library

Range access begin cbegin   end cend rbegin crbegin   rend crend size ssize   data cdata empty

Range conversions std::from_range_t std::from_range (C++23)(C++23)     to (C++23)

Dangling iterator handling dangling borrowed_iterator_t borrowed_subrange_t

Range primitives
range_size_trange_difference_trange_value_t elements_of (C++23)	iterator_tconst_iterator_tsentinel_tconst_sentinel_t (C++23)(C++23)	range_reference_trange_const_reference_trange_rvalue_reference_trange_common_reference_t (C++23)

Range concepts
range borrowed_range    sized_range	common_range view viewable_range	input_range output_range forward_range	bidirectional_range    random_access_range contiguous_range	constant_range (C++23)

Views
view_interface	subrange

Range factories
empty_viewviews::empty	single_viewviews::single	basic_istream_viewviews::istream	iota_viewviews::iota	repeat_viewviews::repeat (C++23)(C++23)

Range adaptors
views::all_tviews::all ref_view owning_view as_rvalue_viewviews::as_rvalue (C++23)(C++23)   filter_viewviews::filter transform_viewviews::transform take_viewviews::take take_while_viewviews::take_while concat_viewviews::concat (C++26)(C++26)	drop_viewviews::drop drop_while_viewviews::drop_while join_viewviews::join join_with_viewviews::join_with (C++23)(C++23)   lazy_split_viewviews::lazy_split split_viewviews::split views::counted common_viewviews::common	reverse_viewviews::reverse as_const_viewviews::as_const (C++23)(C++23) elements_viewviews::elements keys_viewviews::keys values_viewviews::values enumerate_viewviews::enumerate (C++23)(C++23) zip_viewviews::zip (C++23)(C++23) zip_transform_viewviews::zip_transform (C++23)(C++23)	adjacent_viewviews::adjacent (C++23)(C++23) views::pairwise (C++23) adjacent_transform_viewviews::adjacent_transform (C++23)(C++23) views::pairwise_transform (C++23) chunk_viewviews::chunk (C++23)(C++23) slide_viewviews::slide (C++23)(C++23) chunk_by_viewviews::chunk_by (C++23)(C++23) stride_viewviews::stride (C++23)(C++23) cartesian_product_viewviews::cartesian_product (C++23)(C++23)

Range generators std::generator (C++23)

Range adaptor closure objects range_adaptor_closure (C++23)

Range adaptor objects

Helper items
copyable-box movable-box (until C++23)  (C++23)	simple-view non-propagating-cache

 

std::ranges::chunk_by_view

Member functions

chunk_by_view::chunk_by_view

chunk_by_view::base

chunk_by_view::pred

chunk_by_view::begin

chunk_by_view::end

chunk_by_view::find_next

chunk_by_view::find_prev

Deduction guides

Iterator

chunk_by_view::iterator::iterator

chunk_by_view::iterator::operator*

chunk_by_view::iterator::operator++ chunk_by_view::iterator::operator++(int) chunk_by_view::iterator::operator-- chunk_by_view::iterator::operator--(int)

operator==(chunk_by_view::iterator)

 

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. The first element of each such pair belongs to the previous chunk, and the second element belongs to the next chunk.

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.

Expression-equivalent

Expression e is expression-equivalent to expression f, if

• e and f have the same effects, and
• either both are constant subexpressions or else neither is a constant subexpression, and
• either both are potentially-throwing or else neither is potentially-throwing (i.e. noexcept(e) == noexcept(f)).

Data members

Typical implementations of chunk_by_view hold three non-static data members:

• the underlying view of type V (shown here as base_ for exposition only),
• a wrapper that wraps the predicate used to split the elements of base_ of type movable-box<Pred> (shown here as pred_ for exposition only), where movable-box is a wrapper class template that always satisfies movable,
• an object of std::optional-like type (shown here as begin_ for exposition only) that caches an iterator to the first element.

Member functions

(constructor)	constructs a chunk_by_view (public member function)
base	returns a copy of the underlying (adapted) view (public member function)
pred	returns a reference to the stored predicate (public member function)
begin	returns an iterator to the beginning (public member function)
end	returns an iterator or a sentinel to the end (public member function)
find_next (C++23)	returns an iterator to the begin of the next subrange (the name is for exposition only) (exposition-only member function*)
find_prev (C++23)	returns an iterator to the begin of the previous subrange (the name is for exposition only) (exposition-only member function*)
Inherited from std::ranges::view_interface
empty	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>)
cbegin (C++23)	returns a constant iterator to the beginning of the range. (public member function of std::ranges::view_interface<D>)
cend (C++23)	returns a sentinel for the constant iterator of the range. (public member function of std::ranges::view_interface<D>)
operator bool	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>)
front	returns the first element in the derived view. Provided if it satisfies forward_range. (public member function of std::ranges::view_interface<D>)
back	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>)

Nested classes

iterator (C++23)

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 object might have unintuitive behavior.

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

Example

A link to test: Compiler Explorer

Run this code

#include <functional>
#include <iostream>
#include <ranges>
#include <string_view>
#include <vector>
 
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()
{
    {
        auto v = std::vector{1, 2, 3, 1, 2, 3, 3, 3, 1, 2, 3};
        auto fun = std::ranges::less{};
        auto view = v | std::views::chunk_by(fun);
        print_chunks(view);
    }
    {
        auto v = std::vector{1, 2, 3, 4, 4, 0, 2, 3, 3, 3, 2, 1};
        auto fun = std::not_fn(std::ranges::equal_to{}); // or ranges::not_equal_to
        auto view = v | std::views::chunk_by(fun);
        print_chunks(view);
    }
    {
        std::string v = "__cpp_lib_ranges_chunk_by";
        auto fun = [](char x, char y) { return not(x == '_' or y == '_'); };
        auto view = v | std::views::chunk_by(fun);
        print_chunks(view, "");
    }
}

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]

References

• C++23 standard (ISO/IEC 14882:2024):

• 26.7.29 Chunk by view [range.chunk.by]

See also

ranges::chunk_viewviews::chunk (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)
ranges::slide_viewviews::slide (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)
ranges::stride_viewviews::stride (C++23)	a view consisting of elements of another view, advancing over N elements at a time (class template) (range adaptor object)