C++ Vector Index Performance

testing.cpp

#include <iostream>
#include <tuple>
#include <vector>
#include <unordered_map>
#include <algorithm>
#include <string>
#include <chrono>

int main() {
  std::unordered_map<int, int> index;
	index.reserve (10000);

	std::vector<std::tuple<int, int>> lin_index;
	lin_index.resize (10000);

	std::vector<big_ass_struct> to_search_vec;
	to_search_vec.resize (10000);

	// Set IDs
	for (int i = 0; i < to_search_vec.size (); ++i) {
		to_search_vec[i].id = i;
	}

	// Randomize
	std::random_shuffle (to_search_vec.begin (), to_search_vec.end ());

	// Create Index
	for (int i = 0; i < to_search_vec.size (); ++i) {
		index[to_search_vec[i].id] = i;
		lin_index.push_back (std::make_tuple(to_search_vec[i].id, i));
	}

	// Create IDs to search for
	std::vector<int> id_s;
	id_s.resize (1000);

	std::vector<int> found_id_s;
	found_id_s.resize (1000);

	for (int i = 0; i < id_s.size (); ++i) {
		id_s[i] = i;
	}

	std::random_shuffle (id_s.begin (), id_s.end ());

	// Without index
	auto start_1 = std::chrono::high_resolution_clock::now ();

	for (int id : id_s) {
		for (auto& ele : to_search_vec) {
			if (ele.id == id) {
				found_id_s.push_back (ele.id);
			}
		}
	}

	auto end_1 = std::chrono::high_resolution_clock::now ();

	auto dur_1 = end_1 - start_1;

	std::cout <<  dur_1.count () << "\r\n";

	// Cleanup
	found_id_s.clear ();

	// With Index
	auto start_2 = std::chrono::high_resolution_clock::now ();

	for (int id : id_s) {
		int pos = index[id];

		auto& ele = to_search_vec[pos];

		found_id_s.push_back (ele.id);
	}

	auto end_2 = std::chrono::high_resolution_clock::now ();

	auto dur_2 = end_2 - start_2;

	std::cout << dur_2.count () << "\r\n";

	// With linear Index
	auto start_3 = std::chrono::high_resolution_clock::now ();

	for (int id : id_s) {
		for (auto& ind : lin_index) {
			int index_id = std::get<0> (ind);
			if (index_id == id) {
				int index_index = std::get<1> (ind);
				found_id_s.push_back (to_search_vec[index_index].id);
			}
		}
	}

	auto end_3 = std::chrono::high_resolution_clock::now ();

	auto dur_3 = end_3 - start_3;

	std::cout << dur_3.count () << "\r\n";

	int bla;
	std::cin >> bla;
}