[英]STXXL: How to sort Vector of pairs on second element?
Similar Question is available here: How do I sort a vector of pairs based on the second element of the pair? 这里有类似的问题: 如何根据对的第二个元素对向量进行排序? but I am interested in External Memory Sorting.
但我对外部存储器排序感兴趣。
I have tried using the analogies from Internal Memory Sorting but the error occurs in sorter_stream.h file of STXXL as: 我尝试使用内部存储器排序中的类比,但是在STXXL的sorter_stream.h文件中出现错误,如下所示:
My code : 我的代码:
#include <iostream>
#include <stxxl/vector>
#include <stxxl/sorter>
#include <limits>
using namespace std;
typedef std::pair<int,int> my_pair;
struct my_comparator
{
bool operator()(const my_pair& left, const my_pair& right)
{
return left.first < right.first;
}
int min_value() const
{
return std::numeric_limits<int>::min();
}
int max_value() const
{
return std::numeric_limits<int>::max();
}
};
int main()
{
typedef stxxl::sorter<my_pair, my_comparator> sorter_type;
sorter_type int_sorter(my_comparator(), 64 * 1024 * 1024);
for (int i = 10; i > 0; i--)
{
int_sorter.push(my_pair(i,i+10));
}
int_sorter.sort(); // sort elements (in ascending order)
while (!int_sorter.empty())
{
std::cout << (*int_sorter).first << " "<<(*int_sorter).second<<endl;
++int_sorter;
}
return 0;
}
Error : 错误:
sort_stream.h(481): error C2679: binary '=' : no operator found which takes a right-hand operand of type 'int' (or there is no acceptable conversion)
UPDATE: 更新:
Changing the return type of min_value(),max_value() function to my_pair as: 将min_value(),max_value()函数的返回类型更改为my_pair,方法是:
struct my_comparator
{
bool operator()(const my_pair& left, const my_pair& right)
{
return left.first < right.first;
}
my_pair min_value() const
{
return my_pair(std::numeric_limits<int>::min(),std::numeric_limits<int>::min());
}
my_pair max_value() const
{
return my_pair(std::numeric_limits<int>::max(),std::numeric_limits<int>::max());
}
};
gives the following Error: 给出以下错误:
sort_helper.h(94): error C3848: expression having type 'const my_comparator' would lose some const-volatile qualifiers in order to call 'bool my_comparator::operator ()(const my_pair &,const my_pair &)'
PS : Being a novice (Reputation<50) , I am not allowed to comment, that's why writing a new Question. PS:作为一个新手(Reputation <50),我不允许发表评论,这就是为什么要写一个新问题。
Got the following example in STXXL:Sorter Section which addresses the same problem. 在STXXL:Sorter部分中获得了以下示例,该示例解决了相同的问题。
Code: 码:
#include <stxxl/sorter>
#include <stxxl/stats>
#include <stxxl/timer>
#include <stxxl/random>
#include <limits>
struct TwoInteger
{
int i, j;
TwoInteger()
{ }
TwoInteger(int _i, int _j)
: i(_i), j(_j)
{ }
};
struct TwoIntegerComparator
{
bool operator () (const TwoInteger& a, const TwoInteger& b) const
{
return a.i < b.i;
}
TwoInteger min_value() const
{
return TwoInteger(std::numeric_limits<int>::min(), std::numeric_limits<int>::min());
}
TwoInteger max_value() const
{
return TwoInteger(std::numeric_limits<int>::max(), std::numeric_limits<int>::max());
}
};
int main()
{
// template parameter <ValueType, CompareType, BlockSize(optional), AllocStr(optional)>
typedef stxxl::sorter<TwoInteger, TwoIntegerComparator, 1*1024*1024> sorter_type;
// create sorter object (CompareType(), MainMemoryLimit)
sorter_type int_sorter(TwoIntegerComparator(), 64 * 1024 * 1024);
stxxl::random_number32 rand32;
stxxl::timer Timer1;
Timer1.start();
// insert random numbers from [0,100000)
for (size_t i = 0; i < 1000; ++i)
{
int_sorter.push(TwoInteger(rand32() % 100000, (int)i)); // fill sorter container
}
Timer1.stop();
STXXL_MSG("push time: " << (Timer1.mseconds() / 1000));
stxxl::timer Timer2;
Timer2.start();
int_sorter.sort(); // switch to output state and sort
Timer2.stop();
STXXL_MSG("sort time: " << (Timer2.mseconds() / 1000));
// echo sorted elements
while (!int_sorter.empty())
{
std::cout << int_sorter->i << " "; // access value
++int_sorter;
}
return 0;
}
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