docs/Frequency/FrequentItemsCppExample.md

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# Frequent Items Sketch C++ Example

    #include <iostream>
    #include <fstream>

    #include <frequent_items_sketch.hpp>

    //simplified file operations and no error handling for clarity
    int main(int argc, char **argv) {
      typedef datasketches::frequent_items_sketch<std::string> frequent_strings_sketch;

      // this section generates two sketches and serializes them into files
      {
        frequent_strings_sketch sketch1(64);
        sketch1.update("a");
        sketch1.update("a");
        sketch1.update("b");
        sketch1.update("c");
        sketch1.update("a");
        sketch1.update("d");
        sketch1.update("a");
        std::ofstream os1("freq_str_sketch1.bin");
        sketch1.serialize(os1);

        frequent_strings_sketch sketch2(64);
        sketch2.update("e");
        sketch2.update("a");
        sketch2.update("f");
        sketch2.update("f");
        sketch2.update("f");
        sketch2.update("g");
        sketch2.update("a");
        sketch2.update("f");
        std::ofstream os2("freq_str_sketch2.bin");
        sketch2.serialize(os2);
      }

      // this section deserializes the sketches, produces a union and prints the result
      {
        std::ifstream is1("freq_str_sketch1.bin");
        frequent_strings_sketch sketch1 = frequent_strings_sketch::deserialize(is1);

        std::ifstream is2("freq_str_sketch2.bin");
        frequent_strings_sketch sketch2 = frequent_strings_sketch::deserialize(is2);

        // we could merge sketch2 into sketch1 or the other way around
        // this is an example of using a new sketch as a union and keeping the original sketches intact
        frequent_strings_sketch u(64);
        u.merge(sketch1);
        u.merge(sketch2);

        auto items = u.get_frequent_items(datasketches::NO_FALSE_POSITIVES);
        std::cout << "Frequent strings: " << items.size() << std::endl;
        std::cout << "Str\tEst\tLB\tUB" << std::endl;
        for (auto row: items) {
          std::cout << row.get_item() << "\t" << row.get_estimate() << "\t"
            << row.get_lower_bound() << "\t" << row.get_upper_bound() << std::endl;
        }
      }

      return 0;
    }

    Output:
    Frequent strings: 7
    Str	Est	LB	UB
    a	6	6	6
    f	4	4	4
    c	1	1	1
    d	1	1	1
    e	1	1	1
    b	1	1	1
    g	1	1	1