std::ranges::transform, std::ranges::unary_transform_result, std::ranges::binary_transform_result

Since C++20

Header: <algorithm>

Applies the given function to a range and stores the result in another range, beginning at result.

# Declarations

Call signature

template< std::input_iterator I, std::sentinel_for<I> S, std::weakly_incrementable O,
std::copy_constructible F, class Proj = std::identity >
requires std::indirectly_writable<O,
std::indirect_result_t<F&, std::projected<I, Proj>>>
constexpr unary_transform_result<I, O>
transform( I first1, S last1, O result, F op, Proj proj = {} );

(since C++20)

template< ranges::input_range R, std::weakly_incrementable O,
std::copy_constructible F, class Proj = std::identity >
requires std::indirectly_writable<O,
std::indirect_result_t<F&, std::projected<ranges::iterator_t<R>, Proj>>>
constexpr unary_transform_result<ranges::borrowed_iterator_t<R>, O>
transform( R&& r, O result, F op, Proj proj = {} );

(since C++20)

template< std::input_iterator I1, std::sentinel_for<I1> S1,
std::input_iterator I2, std::sentinel_for<I2> S2,
std::weakly_incrementable O,
std::copy_constructible F,
class Proj1 = std::identity, class Proj2 = std::identity >
requires std::indirectly_writable<O,
std::indirect_result_t<F&,
std::projected<I1, Proj1>,
std::projected<I2, Proj2>>>
constexpr binary_transform_result<I1, I2, O>
transform( I1 first1, S1 last1, I2 first2, S2 last2, O result,
F binary_op, Proj1 proj1 = {}, Proj2 proj2 = {} );

(since C++20)

template< ranges::input_range R1,
ranges::input_range R2,
std::weakly_incrementable O,
std::copy_constructible F,
class Proj1 = std::identity, class Proj2 = std::identity >
requires std::indirectly_writable<O,
std::indirect_result_t<F&,
std::projected<ranges::iterator_t<R1>, Proj1>,
std::projected<ranges::iterator_t<R2>, Proj2>>>
constexpr binary_transform_result<ranges::borrowed_iterator_t<R1>,
ranges::borrowed_iterator_t<R2>, O>
transform( R1&& r1, R2&& r2, O result, F binary_op,
Proj1 proj1 = {}, Proj2 proj2 = {} );

(since C++20)

Helper types

template< class I, class O >
using unary_transform_result = ranges::in_out_result<I, O>;

(since C++20)

template< class I1, class I2, class O >
using binary_transform_result = ranges::in_in_out_result<I1, I2, O>;

(since C++20)

# Parameters

# Notes

ranges::transform does not guarantee in-order application of op or binary_op. To apply a function to a sequence in-order or to apply a function that modifies the elements of a sequence, use ranges::for_each.

# Example

#include <algorithm>
#include <cctype>
#include <functional>
#include <iostream>
#include <string>
#include <vector>
 
int main()
{
    std::string s{"hello"};
    auto op = [](unsigned char c) -> unsigned char { return std::toupper(c); };
 
    namespace ranges = std::ranges;
 
    // uppercase the string in-place
    ranges::transform(s.begin(), s.end(), s.begin(), op );
 
    std::vector<std::size_t> ordinals;
    // convert each char to size_t
    ranges::transform(s, std::back_inserter(ordinals),
                      [](unsigned char c) -> std::size_t { return c; });
 
    std::cout << s << ':';
    for (auto ord : ordinals)
        std::cout << ' ' << ord;
 
    // double each ordinal
    ranges::transform(ordinals, ordinals, ordinals.begin(), std::plus {});
 
    std::cout << '\n';
    for (auto ord : ordinals)
        std::cout << ord << ' ';
    std::cout << '\n';
 
    struct Foo
    {
        char bar;
    };
    const std::vector<Foo> f = {{'h'},{'e'},{'l'},{'l'},{'o'}};
    std::string result;
    // project, then uppercase
    ranges::transform(f, std::back_inserter(result), op, &Foo::bar);
    std::cout << result << '\n';
}

# See also