我正在为我的妻子编写一个程序，以帮助我们尝试确定她应申请的医学院。但是，我遇到了一个问题，我试图提取在4种不同情况下出现在前20名成绩中的学校。
例如，在其中一种情况下，我将城市的中位数收入除以城市的平均房价。返回一个双精度数，然后创建一个新向量，然后根据该数字从最高到最低对该向量进行排序。而且我对池中的其他3个媒介进行了类似的操作，并应用了不同的情况。
我知道我可以蛮力地用嵌套的for循环提取名称，但是我很好奇是否有办法快速有效地做到这一点。到目前为止，这是我的尝试。 （请注意，这只是一个示例，我的实际代码中有30所学校。）
#include <algorithm>
#include <iterator>
#include <iostream>
#include <memory>
#include <string>
#include <vector>
struct Schools
{
Schools(std::string n = "", double h = 0.0, double t = 0.0, int r = 0, int w = 0) : name(n), housing(h), tuition(t), rank(r), weight(w){};
std::string name;
double housing;
double tuition;
int rank;
int weight;
};
void load(std::vector<std::shared_ptr<Schools>> &v, std::string n, double h, double t, int r, int w)
{
auto newSchool = std::make_shared<Schools>(n,h,t,r,w);
v.emplace_back(newSchool);
}
void init(std::vector<std::shared_ptr<Schools>> &schools)
{
load(schools,"School1",40.3,20.0,3,6);
load(schools,"School2",10.3,10.4,5,1);
load(schools,"School3",33.3,23.5,1,2);
load(schools,"School4",8.5,15.5,4,8);
}
auto findIntersection(auto &a, auto &b)
{
std::vector<std::shared_ptr<Schools>> in;
std::set_intersection(begin(a),end(a),begin(b),end(b),std::back_inserter(in));
return in;
}
auto findCommon(auto &housing, auto &tuition, auto &rank, auto &weight)
{
std::vector<std::shared_ptr<Schools>> inCommon;
inCommon = findIntersection(housing,tuition);
inCommon = findIntersection(inCommon,rank);
inCommon = findIntersection(inCommon,weight);
return inCommon;
}
bool compareHM(const std::shared_ptr<Schools> &a, const std::shared_ptr<Schools> &b)
{
return a->housing < b->housing;
}
bool compareT(const std::shared_ptr<Schools> &a, const std::shared_ptr<Schools> &b)
{
return a->tuition < b->tuition;
}
bool compareRank(const std::shared_ptr<Schools> &a, const std::shared_ptr<Schools> &b)
{
return a->rank > b->rank;
}
bool compareWeight(const std::shared_ptr<Schools> &a, const std::shared_ptr<Schools> &b)
{
return a->weight > b->weight;
}
int main()
{
std::vector<std::shared_ptr<Schools>> schools;
init(schools);
std::vector<std::shared_ptr<Schools>> sortByHousing = schools;
std::vector<std::shared_ptr<Schools>> sortByTuition = schools;
std::vector<std::shared_ptr<Schools>> sortByRank = schools;
std::vector<std::shared_ptr<Schools>> sortByWeight = schools;
std::sort(begin(sortByHousing),end(sortByHousing), compareHM);
std::sort(begin(sortByTuition),end(sortByTuition), compareT);
std::sort(begin(sortByRank),end(sortByRank), compareRank);
std::sort(begin(sortByWeight),end(sortByWeight), compareWeight);
std::vector<std::shared_ptr<Schools>> commonSchools = findCommon(sortByHousing,sortByTuition,sortByRank,sortByWeight);
for (auto && e: commonSchools)
{
std::cout << e->name << std::endl;
}
}
当我尝试使用std::set_intersection时遇到问题，然后我很快意识到我无法做类似begin(a)->name的事情。同样，我尝试提取在我所遇到的4种情况中都出现的通用名称。我该如何实施呢？我对std::set_intersection的想法是否太遥远？
谢谢！
编辑：
这是我的functionThatCompares
bool compareTuition(const std::shared_ptr<Schools> &a, const std::shared_ptr<Schools> &b)
{
return a->tuition < b->tuition;
}
编辑2：示例输出
The top 20 sorted by Median/House are:
Name of Institution Median/House Price Tuition Over 8 Years Has Space Industry? Score
University of Alabama 0.463577 0.722279 1 0.641825
University of Maryland 0.38124 0.722617 1 0.527583
Johns Hopkins Univerty School of Medicine 0.38124 0.606103 1 0.629002
Indiana University 0.335939 0.501944 0 0.669276
Ohio State University 0.32499 0.610704 1 0.532156
Perelman School of Medicine 0.26908 0.653143 1 0.411977
Duke University School of Medicine 0.246991 0.66683 1 0.370395
University of Wisconsin 0.226581 0.64686 0 0.350278
Chicago Medical School 0.221883 0.648157 0 0.342329
Northwestern University 0.221883 0.677341 0 0.32758
Case Western Reserve 0.211817 0.536384 1 0.394898
Emory University 0.206169 0.576814 1 0.357427
Geisel School of Medicine 0.205529 0.71526 0 0.287349
University of Massachusetts 0.19562 0.64686 1 0.302414
Medical University of SC 0.185816 0.354728 0 0.523827
University of North Carolina 0.176684 0.6637 0 0.26621
University of Michigan Medical School 0.158465 0.637237 1 0.248675
Rutgers New Jersey Medical School 0.140412 0.722115 0 0.194446
University of Utah 0.140142 0.311285 0 0.450205
Georgetown University 0.128883 0.604001 1 0.213382
The top 20 sorted by Tuition are:
Name of Institution Median/House Price Tuition Over 8 Years Has Space Industry? Score
University of Utah 0.140142 0.311285 0 0.450205
Medical University of SC 0.185816 0.354728 0 0.523827
University of California, LA 0.07633 0.47547 1 0.160536
Indiana University 0.335939 0.501944 0 0.669276
University of California, SD 0.109214 0.531397 1 0.205523
Case Western Reserve 0.211817 0.536384 1 0.394898
Emory University 0.206169 0.576814 1 0.357427
Icahn School of Medicine 0.0822029 0.585946 1 0.140291
Georgetown University 0.128883 0.604001 1 0.213382
Johns Hopkins Univerty School of Medicine 0.38124 0.606103 1 0.629002
Ohio State University 0.32499 0.610704 1 0.532156
University of Virgina School of Medicine 0.123755 0.630067 1 0.196415
University of Michigan Medical School 0.158465 0.637237 1 0.248675
NY University School of Medicine 0.0822029 0.642516 1 0.127939
Tufts University School of Medicine 0.100302 0.644314 1 0.155672
University of Massachusetts 0.19562 0.64686 1 0.302414
University of Wisconsin 0.226581 0.64686 0 0.350278
Chicago Medical School 0.221883 0.648157 0 0.342329
Perelman School of Medicine 0.26908 0.653143 1 0.411977
Standford University School of Medicine 0.0780054 0.656658 1 0.118791
The top 20 sorted by Median/House and Loweset Tution are:
Name of Institution Median/House Price Tuition Over 8 Years Has Space Industry? Score
University of Maryland 0.38124 0.722617 1 0.527583
Chicago Medical School 0.221883 0.648157 0 0.342329
University Of Washington 0.0973689 0.761413 1 0.127879
University of Alabama 0.463577 0.722279 1 0.641825
Rutgers New Jersey Medical School 0.140412 0.722115 0 0.194446
Geisel School of Medicine 0.205529 0.71526 0 0.287349
Ohio State University 0.32499 0.610704 1 0.532156
Harvard Medical School 0.100302 0.710787 1 0.141114
Duke University School of Medicine 0.246991 0.66683 1 0.370395
Boston University School of Medicine 0.100302 0.710787 1 0.141114
Perelman School of Medicine 0.26908 0.653143 1 0.411977
University of Wisconsin 0.226581 0.64686 0 0.350278
University of North Carolina 0.176684 0.6637 0 0.26621
Standford University School of Medicine 0.0780054 0.656658 1 0.118791
Johns Hopkins Univerty School of Medicine 0.38124 0.606103 1 0.629002
Northwestern University 0.221883 0.677341 0 0.32758
Indiana University 0.335939 0.501944 0 0.669276
Case Western Reserve 0.211817 0.536384 1 0.394898
Emory University 0.206169 0.576814 1 0.357427
University of Massachusetts 0.19562 0.64686 1 0.302414
The top 20 sorted by Score (Median/House * Tuition/Salary) are:
Name of Institution Median/House Price Tuition Over 8 Years Has Space Industry? Score
Indiana University 0.335939 0.501944 0 0.669276
University of Alabama 0.463577 0.722279 1 0.641825
Johns Hopkins Univerty School of Medicine 0.38124 0.606103 1 0.629002
Ohio State University 0.32499 0.610704 1 0.532156
University of Maryland 0.38124 0.722617 1 0.527583
Medical University of SC 0.185816 0.354728 0 0.523827
University of Utah 0.140142 0.311285 0 0.450205
Perelman School of Medicine 0.26908 0.653143 1 0.411977
Case Western Reserve 0.211817 0.536384 1 0.394898
Duke University School of Medicine 0.246991 0.66683 1 0.370395
Emory University 0.206169 0.576814 1 0.357427
University of Wisconsin 0.226581 0.64686 0 0.350278
Chicago Medical School 0.221883 0.648157 0 0.342329
Northwestern University 0.221883 0.677341 0 0.32758
University of Massachusetts 0.19562 0.64686 1 0.302414
Geisel School of Medicine 0.205529 0.71526 0 0.287349
University of North Carolina 0.176684 0.6637 0 0.26621
University of Michigan Medical School 0.158465 0.637237 1 0.248675
Georgetown University 0.128883 0.604001 1 0.213382
University of California, SD 0.109214 0.531397 1 0.205523
编辑3：
对于那些尝试编译此程序的人，我深表歉意。现在，它可以编译并运行。
答案 0 :(得分：2)
当您执行诸如sort或set_intersection之类的操作时，可以指定如何进行比较。如果您未指定任何内容，则将使用operator<作为类型（如果已定义）。
在这种情况下，您似乎想使用partial_sort_copy而不是sort。这样一来，您可以按每种排序（例如）获得排名前10的学校。
然后，您必须按名称对它们进行重新排序以进行set_intersection。
然后，您将执行set_intersection以获取这些集合之间的通用学校。
这里有一些演示代码：
#include <iostream>
#include <algorithm>
#include <vector>
#include <memory>
struct School
{
std::string name;
double housing;
double tuition;
int rank;
int weight;
// default comparison to use if nothing else is specified:
bool operator<(School const &other) const { return name < other.name; }
};
int main()
{
std::vector<School> schools{
{"School1", 40.3, 20.0, 3, 6},
{"School2", 10.3, 10.4, 5, 1},
{"School3", 33.3, 23.5, 1, 2},
{"School4", 8.5, 15.5, 4, 8}
};
// We specify the size of each of these as 3, so when we do the
// partial_sort_copy, it'll fill in the top 3 for that category.
std::vector<School> byHousing(3);
std::vector<School> byRank(3);
std::vector<School> byWeight(3);
std::partial_sort_copy(schools.begin(), schools.end(), byHousing.begin(), byHousing.end(),
[](School const &a, School const &b) { return a.housing < b.housing; });
std::partial_sort_copy(schools.begin(), schools.end(), byRank.begin(), byRank.end(),
[](School const &a, School const &b) { return a.rank < b.rank; });
std::partial_sort_copy(schools.begin(), schools.end(), byWeight.begin(), byWeight.end(),
[](School const &a, School const &b) { return a.weight < b.weight; });
std::sort(byHousing.begin(), byHousing.end());
std::sort(byRank.begin(), byRank.end());
std::sort(byWeight.begin(), byWeight.end());
std::vector<School> temp, commonSchools;
std::set_intersection(byHousing.begin(), byHousing.end(), byRank.begin(), byRank.end(),
std::back_inserter(temp));
std::set_intersection(temp.begin(), temp.end(), byWeight.begin(), byWeight.end(),
std::back_inserter(commonSchools));
std::cout << "Common Schools\n";
for (auto const & e: commonSchools)
{
std::cout << e.name << "\n";
}
}
结果：
Common Schools
School3
顺便说一句，在我看来，使用shared_ptr编写代码会增加一些额外的工作（可能没有足够的精力来关心），所以我没有打扰。我还省去了按学费进行的筛选/分类-几乎一样。
答案 1 :(得分：1)
如std::set_intersection文档中所述
3）使用给定的二进制比较函数comp对元素进行比较，并且必须对范围进行排序。
（强调是我的），因此您不能立即将其与向量一起使用，需要在应用name之前将它们全部遵循一个通用准则，例如使用std::set_intersection。为std::set_intersection本身提供相同的比较器
我将为每所学校创建一个权重，并使其根据每个向量的指数成指数增长，然后将它们求和并基于该值进行排序。获胜最少的人。您还可以在排序决策中添加用于增加/减少某些条件的权重的系数：
std::unordered_map<std::shared_ptr<Schools>,double> weights;
size_t count = 0;
auto weightCalc = [&weights, &count]( std::shared_ptr<Schools> s ) {
weights[s] += std::exp( count++ );
};
std::for_each( sortByHousing.begin(), sortByHousing.end(), weightCalc );
count = 0;
std::for_each( sortByTuition.begin(), sortByTuition.end(), weightCalc );
count = 0;
std::for_each( sortByRank.begin(), sortByRank.end(), weightCalc );
count = 0;
std::for_each( sortByWeight.begin(), sortByWeight.end(), weightCalc );
std::multimap<double,std::shared_ptr<Schools>> sortedSchools;
std::copy( weights.begin(), weights.end(), std::inserter( sortedSchools ), []( const auto &p ) { return std::make_pair( p.second, p.first ); } );
然后使用sortedSchools的前n所学校