# std::ranges::remove_copy, std::ranges::remove_copy_if, std::ranges::remove_copy_result, std::ranges::remove_copy_if_result

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< cpp‎ | algorithm‎ | ranges

Defined in header `<algorithm>` |  |
Call signature |  |
template< std::input_iterator I, std::sentinel_for<I> S, std::weakly_incrementable O, class T, class Proj = std::identity > requires std::indirectly_copyable<I, O> && std::indirect_binary_predicate<ranges::equal_to, std::projected<I, Proj>, const T*> constexpr remove_copy_result<I, O> remove_copy( I first, S last, O result, const T& value, Proj proj = {} ); | (1) | (since C++20)
template< ranges::input_range R, std::weakly_incrementable O, class T, class Proj = std::identity > requires std::indirectly_copyable<ranges::iterator_t<R>, O> && std::indirect_binary_predicate<ranges::equal_to, std::projected<ranges::iterator_t<R>, Proj>, const T*> constexpr remove_copy_result<ranges::borrowed_iterator_t<R>, O> remove_copy( R&& r, O result, const T& value, Proj proj = {} ); | (2) | (since C++20)
template< std::input_iterator I, std::sentinel_for<I> S, std::weakly_incrementable O, class Proj = std::identity, std::indirect_unary_predicate<std::projected<I, Proj>> Pred > requires std::indirectly_copyable<I, O> constexpr remove_copy_if_result<I, O> remove_copy_if( I first, S last, O result, Pred pred, Proj proj = {} ); | (3) | (since C++20)
template< ranges::input_range R, std::weakly_incrementable O, class Proj = std::identity, std::indirect_unary_predicate< std::projected<ranges::iterator_t<R>, Proj>> Pred > requires std::indirectly_copyable<ranges::iterator_t<R>, O> constexpr remove_copy_if_result<ranges::borrowed_iterator_t<R>, O> remove_copy_if( R&& r, O result, Pred pred, Proj proj = {} ); | (4) | (since C++20)
Helper types |  |
template< class I, class O > using remove_copy_result = ranges::in_out_result<I, O>; | (5) | (since C++20)
template< class I, class O > using remove_copy_if_result = ranges::in_out_result<I, O>; | (6) | (since C++20)

Copies elements from the source range `[`first`,` last`)`, to the destination range beginning at result, omitting the elements which (after being projected by proj) satisfy specific criteria. The behavior is undefined if the source and destination ranges overlap.

1) Ignores all elements that are equal to value.
3) Ignores all elements for which predicate pred returns true.
2,4) Same as (1,3), but uses r as the source range, as if using ranges::begin(r) as first, and ranges::end(r) as last.

The function-like entities described on this page are niebloids, that is:

- Explicit template argument lists cannot be specified when calling any of them.
- None of them are visible to argument-dependent lookup.
- When any of them are found by normal unqualified lookup as the name to the left of the function-call operator, argument-dependent lookup is inhibited.

In practice, they may be implemented as function objects, or with special compiler extensions.

### Parameters

first, last | - | the source range of elements
r | - | the source range of elements
result | - | the beginning of the destination range
value | - | the value of the elements not to copy
comp | - | the binary predicate to compare the projected elements
proj | - | the projection to apply to the elements

### Return value

{last, result + N}, where `N` is the number of elements copied.

### Complexity

Exactly ranges::distance(first, last) applications of the corresponding predicate comp and any projection proj.

### Notes

The algorithm is stable, i.e. preserves the relative order of the copied elements.

### Possible implementation

remove_copy
    struct remove_copy_fn
    {
        template<std::input_iterator I, std::sentinel_for<I> S, std::weakly_incrementable O,
                 class T, class Proj = std::identity>
        requires std::indirectly_copyable<I, O> &&
                 std::indirect_binary_predicate<ranges::equal_to,
                                                std::projected<I, Proj>, const T*>
        constexpr ranges::remove_copy_result<I, O>
            operator()(I first, S last, O result, const T& value, Proj proj = {}) const
        {
            for (; !(first == last); ++first)
            {
                if (value != std::invoke(proj, *first))
                {
                    *result = *first;
                    ++result;
                }
            }
            return {std::move(first), std::move(result)};
        }

        template<ranges::input_range R, std::weakly_incrementable O, class T,
                 class Proj = std::identity>
        requires std::indirectly_copyable<ranges::iterator_t<R>, O> &&
                 std::indirect_binary_predicate<ranges::equal_to,
                 std::projected<ranges::iterator_t<R>, Proj>, const T*>
        constexpr ranges::remove_copy_result<ranges::borrowed_iterator_t<R>, O>
            operator()(R&& r, O result, const T& value, Proj proj = {}) const
        {
            return (*this)(ranges::begin(r), ranges::end(r), std::move(result), value,
                           std::move(proj));
        }
    };

    inline constexpr remove_copy_fn remove_copy {};
remove_copy_if
    struct remove_copy_if_fn
    {
        template<std::input_iterator I, std::sentinel_for<I> S, std::weakly_incrementable O,
                 class Proj = std::identity,
                 std::indirect_unary_predicate<std::projected<I, Proj>> Pred>
        requires std::indirectly_copyable<I, O>
        constexpr ranges::remove_copy_if_result<I, O>
            operator()(I first, S last, O result, Pred pred, Proj proj = {}) const
        {
            for (; first != last; ++first)
            {
                if (false == std::invoke(pred, std::invoke(proj, *first)))
                {
                    *result = *first;
                    ++result;
                }
            }
            return {std::move(first), std::move(result)};
        }

        template<ranges::input_range R, std::weakly_incrementable O,
                 class Proj = std::identity,
                 std::indirect_unary_predicate<
                     std::projected<ranges::iterator_t<R>, Proj>> Pred>
        requires std::indirectly_copyable<ranges::iterator_t<R>, O>
        constexpr ranges::remove_copy_if_result<ranges::borrowed_iterator_t<R>, O>
            operator()(R&& r, O result, Pred pred, Proj proj = {}) const
        {
            return (*this)(ranges::begin(r), ranges::end(r), std::move(result),
                           std::move(pred), std::move(proj));
        }
    };

    inline constexpr remove_copy_if_fn remove_copy_if {};

### Example

Run this code

    #include <algorithm>
    #include <array>
    #include <complex>
    #include <iomanip>
    #include <iostream>
    #include <iterator>
    #include <string_view>
    #include <vector>

    void print(const auto rem, const auto& v)
    {
        std::cout << rem << ' ';
        for (const auto& e : v)
            std::cout << e << ' ';
        std::cout << '\n';
    }

    int main()
    {
        // Filter out the hash symbol from the given string.
        const std::string_view str {"#Small #Buffer #Optimization"};
        std::cout << "before: " << std::quoted(str) << '\n';

        std::cout << "after:  \"";
        std::ranges::remove_copy(str.begin(), str.end(),
                                 std::ostream_iterator<char>(std::cout), '#');
        std::cout << "\"\n";

        // Copy only the complex numbers with positive imaginary part.
        using Ci = std::complex<int>;
        constexpr std::array<Ci, 5> source
        {
            Ci {1, 0}, Ci {0, 1}, Ci {2, -1}, Ci {3, 2}, Ci {4, -3}
        };
        std::vector<std::complex<int>> target;

        std::ranges::remove_copy_if(
            source,
            std::back_inserter(target),
            [](int imag) { return imag <= 0; },
            [](Ci z) { return z.imag(); }
        );

        print("source:", source);
        print("target:", target);
    }

Output:

    before: "#Small #Buffer #Optimization"
    after:  "Small Buffer Optimization"
    source: (1,0) (0,1) (2,-1) (3,2) (4,-3)
    target: (0,1) (3,2)

### See also

ranges::remove ranges::remove_if (C++20)(C++20) | removes elements satisfying specific criteria (niebloid)
ranges::copy ranges::copy_if (C++20)(C++20) | copies a range of elements to a new location (niebloid)
ranges::copy_n (C++20) | copies a number of elements to a new location (niebloid)
ranges::copy_backward (C++20) | copies a range of elements in backwards order (niebloid)
ranges::replace_copy ranges::replace_copy_if (C++20)(C++20) | copies a range, replacing elements satisfying specific criteria with another value (niebloid)
ranges::reverse_copy (C++20) | creates a copy of a range that is reversed (niebloid)
ranges::rotate_copy (C++20) | copies and rotate a range of elements (niebloid)
ranges::unique_copy (C++20) | creates a copy of some range of elements that contains no consecutive duplicates (niebloid)
remove_copy remove_copy_if | copies a range of elements omitting those that satisfy specific criteria (function template)

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