How do I find elements with custom comparators with std::unordered_map for large datasets?

Finding elements using custom comparators in a large dataset with std::unordered_map can be tricky because this data structure relies on hash functions rather than comparators. However, by defining a custom hash function and equality function, you can effectively use std::unordered_map to handle complex data types as keys. Below is an example of how to accomplish this.

unordered_map, custom comparator, hash function, C++, large datasets

This example demonstrates how to create an std::unordered_map with a custom key type using a custom hash function and equality comparator for large datasets.


        #include <iostream>
        #include <unordered_map>
        #include <string>

        struct CustomKey {
            std::string key1;
            int key2;

            bool operator==(const CustomKey &other) const {
                return key1 == other.key1 && key2 == other.key2;
            }
        };

        struct CustomHash {
            std::size_t operator()(const CustomKey &k) const {
                return std::hash<std::string>()(k.key1) ^ (std::hash<int>()(k.key2) << 1);
            }
        };

        int main() {
            std::unordered_map<CustomKey, std::string, CustomHash> custom_map;

            custom_map[{"example", 1}] = "Value 1";
            custom_map[{"example", 2}] = "Value 2";

            CustomKey key_to_find = {"example", 1};
            std::cout << "Found: " << custom_map[key_to_find] << std::endl;

            return 0;
        }

How do I find elements with custom comparators with std::unordered_map for large datasets?

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How do I find elements with custom comparators with std::unordered_map for large datasets?

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