cpp_modern/GeneralSnippets/Transform/Transform.cpp at master · pelocpp/cpp_modern · GitHub

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// =====================================================================================
// Transform.cpp // std::transform
// =====================================================================================

module modern_cpp:transform;

namespace AlgorithmTransform {

    static void test_01()
    {
        // very simple phone book
        std::cout << "List of Entries: " << std::endl;

        std::unordered_map<std::string, std::size_t> phonebook
        {
            { "Hans Meier" ,     12345678 },
            { "Franz Schneider", 81726354 },
            { "Hubert Mueller",  87654321 }
        };

        for (const auto& [name, number] : phonebook) {
            std::cout << name << ": " << number << std::endl;
        }

        std::vector<std::string> names(phonebook.size());  // set size of vector (!)

        // std::transform on a single range - retrieve names from phonebook
        std::transform(
            phonebook.begin(),
            phonebook.end(),
            names.begin(),      // beginning of the destination range
            [](const std::pair<const std::string, std::size_t>& entry) {
                return std::get<0>(entry);
            }
        );

        std::cout << "List of Persons: " << std::endl;
        for (const auto& name : names) {
            std::cout << name << std::endl;
        }
    }

    static void test_02()
    {
        // very simple phone book
        std::cout << "List of Entries: " << std::endl;

        std::unordered_map<std::string, std::size_t> phonebook
        {
            { "Hans Meier" ,      12345678 },
            { "Franz Schneider",  81726354 },
            { "Hubert Mueller",   87654321 }
        };

        for (const auto& [name, number] : phonebook) {
            std::cout << name << ": " << number << std::endl;
        }

        std::vector<std::string> names{};    // empty vector (!)

        // std::transform on a single range - retrieve names from phonebook
        std::transform(
            phonebook.begin(),
            phonebook.end(),
            std::back_inserter(names),   // back_inserter needed (!)
            [](const std::pair<const std::string, std::size_t>& entry) {
                return std::get<0>(entry);
            }
        );

        std::cout << "List of Persons: " << std::endl;
        for (const auto& name : names) {
            std::cout << name << std::endl;
        }
    }

    static void test_03()
    {
        std::vector<std::string> persons
        {
            std::string{ "Hans Meier" },
            std::string{ "Hubert Mueller" },
            std::string{ "Franz Schneider" }
        };

        std::vector<std::size_t> numbers{ 12345678, 7654321, 81726354 };

        std::unordered_map<std::string, std::size_t> contacts{};

        // std::transform on two ranges - create contacts from separate informations
        std::transform(
            persons.cbegin(),
            persons.cend(),
            numbers.begin(),
            std::inserter(contacts, contacts.end()),
            [](const std::string& person, std::size_t number) {
                return std::pair<const std::string, std::size_t>{ person, number };
            }
        );

        std::cout << "List of Contacts: " << std::endl;
        for (const auto& [name, number] : contacts) {
            std::cout << name << ": " << number << std::endl;
        }
    }
}

void main_transform()
{
    using namespace AlgorithmTransform;
    test_01();
    test_02();
    test_03();
}

// =====================================================================================
// End-of-File
// =====================================================================================