std::replace_copy, std::replace_copy_if

Example

print_seq: (seq) = {
    for seq do (e) {
        std::cout << "(e)$ ";
    }
    std::cout << '\n';
}

main: () = {
    src: std::vector<short> = (3, 1, 4, 1, 5, 9, 2, 6, 5);
    print_seq(src);
    dst:= std::vector<int>(src.size());
    std::replace_copy_if(src.cbegin(), src.cend(),
                         dst.begin(),
                         :(n: short) n > 5, 0);
    print_seq(dst);

    src2: std::vector = (
        :std::complex<double>=(1, 3),
        :std::complex<double>=(2, 4),
        :std::complex<double>=(3, 5));
    print_seq(src2);

    dst2:= std::vector<std::complex<double>>(src2.size());
    std::replace_copy_if(src2.cbegin(), src2.cend(),
                         dst2.begin(),
                         :(z: std::complex<double>) std::abs(z) < 5,
                         std::complex<double>(4, 2));
    print_seq(dst2);
}

Output

3 1 4 1 5 9 2 6 5 
3 1 4 1 5 0 2 0 5 
(1,3) (2,4) (3,5) 
(4,2) (4,2) (3,5) 