我正在尝试将图的一些信息存储在unordered_map中。每条边都有一些参数。总共有120条边,每条边有90 * 2个不同的参数。
我有以下std :: unordered_map <>的实现
typedef std::tuple<int, int, int, int> metric_tuple_key; // metric tuple key
// define a hash function for this metric_tuple_key tuple
struct m_KeyHash : public std::unary_function<metric_tuple_key, std::size_t> {
std::size_t operator()(const metric_tuple_key& k) const {
// the magic operation below makes collisions less likely than just the standard XOR
std::size_t seed = std::hash<int>()(std::get<0>(k));
seed ^= std::hash<int>()(std::get<1>(k)) + 0x9e3779b9 + (seed << 6) + (seed >> 2);
seed ^= std::hash<int>()(std::get<2>(k)) + 0x9e3779b97f4a7c15 + (seed << 6) + (seed >> 2);
return seed ^ (std::hash<char>()(std::get<3>(k)) + 0x9e3779b9 + (seed << 6) + (seed >> 2));
}
};
// define the comparison operator for this metric_tuple_key tuple
struct m_KeyEqual : public std::binary_function<metric_tuple_key, metric_tuple_key, bool> {
bool operator()(const metric_tuple_key& v0, const metric_tuple_key& v1) const {
return (std::get<0>(v0) == std::get<0>(v1) && std::get<1>(v0) == std::get<1>(v1) &&
std::get<2>(v0) == std::get<2>(v1) && std::get<3>(v0) == std::get<3>(v1));
}
};
std::unordered_map<metric_tuple_key, double, m_KeyHash, m_KeyEqual> _metrics;
通过创建元组键,我能够将值插入到_metrics
中。
现在,当指定一个键时,我想从_metrics
获取一些值。
//Retrieve around 120 double values. Total number of entries in _metrics is 21600
double k = _metrics.at((std::make_tuple(m, k, edge.first, edge.second))). //do this 120 times
结果表明这非常慢(几乎需要400毫秒)。我希望它只需大约一毫秒或更少的时间。
我是否做错了什么,或者std::unordered_map不适用于我的用例。我以前使用python字典来解决相同的问题,并且在python字典中检索值几乎是瞬间完成的。
编辑:一些unordered_map统计信息:
max_load_factor: 1
size: 21600
bucket_count: 25717
load_factor: 0.839911
编辑:计时器代码:
#include <chrono>
#include <iostream>
#include <iomanip>
class Timer {
private:
std::chrono::time_point<std::chrono::steady_clock> start , stop;;
public:
void startClock();
void stopClock();
void elapsedTime(std::string &message);
};
#include "Timer.hpp"
void Timer::startClock() {
start = std::chrono::steady_clock::now();
}
void Timer::stopClock() {
stop = std::chrono::steady_clock::now();
}
void Timer::elapsedTime(std::string &message) {
auto diff = stop - start;
std::cout << "Elapsed time for " <<message<< " " << std::setprecision(13) <<std::chrono::duration <double, std::milli> (diff).count() << " ms" << std::endl;
}
而时间测量是:
T_met.startClock();
for (const auto& edges: list_of_arcs())
{
double k = _metrics.at((std::make_tuple(m, k, edge.first, edge.second)))
}
T_met.stopClock();
std::tuple
提供的比较运算符有什么问题吗? - Daniel Langr