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问试图用向量排序映射值时令人难以理解的错误
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Stack Overflow用户

提问于 2021-05-02 00:46:36

回答 2查看 43关注 0票数 0

我有一个WordEntry类，它有一个unordered_map<string, int>，我想存储每个单词的频率。我可以这样做，但我也想向用户显示前5个单词和底部5个单词。要做到这一点，我必须整理一下。但是，我得到了一个非常可怕的、令人讨厌的错误，这个错误与您通常的c++异常不一样。我不知道是否包括在内会有很大帮助，因为它是相当长的。这是我的wordentry.h

#ifndef WORDENTRY_H
#define WORDENTRY_H
#include "node.h"
#include "bst.h"
#include <vector>
#include <unordered_map>
#include <string>
#include <algorithm>
using namespace std;

template <class T>
class WordEntry
{
public:
    int retrieveWordFreq(Node<T> *);
    void collectWords(T data);
    void getTop5();
    void getBot5();
    unordered_map<T, int> freqs;

private:
    int freq = 0;
    bool sortByVal( pair<string, int> &a,  pair<string, int> &b);
};

template <class T>
int WordEntry<T>::retrieveWordFreq(Node<T> *word)
{
}

template <class T>
void WordEntry<T>::getTop5()
{
    vector<pair<string, int>> vec;

    // copy key-value pairs from the map to the vector
    unordered_map<string, int>::iterator it2;
    for (it2 = freqs.begin(); it2 != freqs.end(); it2++)
    {
        vec.push_back(make_pair(it2->first, it2->second));
    }

    // // sort the vector by increasing order of its pair's second value
    sort(vec.begin(), vec.end(), sortByVal);

    for (int i = vec.size() - 1; i > vec.size() - 6; i--)
    {
        cout << vec[i].first << ": " << vec[i].second << endl;
    }
}

template <class T>
void WordEntry<T>::getBot5()
{
    vector<pair<string, int>> vec;

     for (auto& it : freqs) {
        vec.push_back(it);
    }

    
    sort(vec.begin(), vec.end(), sortByVal);

    for (int i = 0; i < 6; i++)
    {
        cout << vec[i].first << ": " << vec[i].second << endl;
    }
}

template <class T>
void WordEntry<T>::collectWords(T val)
{
    freqs[val]++;
}

template <class T>
bool WordEntry<T>::sortByVal(pair<string, int> &a,  pair<string, int> &b)
{
    return (a.second < b.second);
}
#endif

还有我的主菜

#include <iostream>
#include <fstream>
#include <string>
#include <vector>
#include <unordered_set>
#include "bst.h"
#include "wordentry.h"


using namespace std;

int main()
{
    fstream file;
    string word, filename;

    BST<string> wordTree; 
    unordered_set<string> set; 
    WordEntry<string> words; 

    filename = "file.txt";
    file.open(filename.c_str());

    
    while (file >> word)
    {
        wordTree.insert(word); 
        words.collectWords(word); 
    } 
    
    cout << "Words amount: " << wordTree.length() << "\n";
    cout << "Unique Words amount: " << set.size() << "\n"; 
    
    words.getBot5(); 

    int choice; 
    
    cout << "What do you want to do?\n1. Enter a word and find it's frequency\n2.Output frequency analysis to a file\n"; 
    cin >> choice; 
    if (choice == 1) {
        string word; 
        cout << "Enter the word you want the frequency of \n"; 
        cin >> word; 
        for (auto x : words.freqs)
        {
            if (x.first == word)
            {
                cout << x.second; 
            }
        }
    }
    else if (choice == 2)
    {
        ofstream outfile ("output.txt"); 
        outfile << "Words amount: " << wordTree.length() << "\n";
        outfile << "Unique Words amount: " << set.size() << "\n"; 
    }
    
    
   return 0; 
    
}

words.getBot5();是罪魁祸首，这意味着我的实现是错误的，但我不知道为什么。我只是将密钥对复制到向量并进行排序。

编辑:这是错误

In file included from c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\bits\stl_algobase.h:71:0,
                 from c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\bits\char_traits.h:39,
                 from c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\ios:40,
                 from c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\ostream:38,
                 from c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\iostream:39,
                 from driver.cpp:1:
c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\bits\predefined_ops.h: In instantiation of 
'constexpr bool __gnu_cxx::__ops::_Iter_comp_iter<_Compare>::operator()(_Iterator1, _Iterator2) [with _Iterator1 = __gnu_cxx::__normal_iterator<std::pair<std::__cxx11::basic_string<char>, int>*, std::vector<std::pair<std::__cxx11::basic_string<char>, int> > 
>; _Iterator2 = __gnu_cxx::__normal_iterator<std::pair<std::__cxx11::basic_string<char>, int>*, std::vector<std::pair<std::__cxx11::basic_string<char>, int> > >; _Compare = bool (WordEntry<std::__cxx11::basic_string<char> >::*)(std::pair<std::__cxx11::basic_string<char>, int>&, std::pair<std::__cxx11::basic_string<char>, int>&)]':
c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\bits\stl_algo.h:1844:14:   required from 'void std::__insertion_sort(_RandomAccessIterator, _RandomAccessIterator, _Compare) [with _RandomAccessIterator = __gnu_cxx::__normal_iterator<std::pair<std::__cxx11::basic_string<char>, int>*, std::vector<std::pair<std::__cxx11::basic_string<char>, int> > >; 
_Compare = __gnu_cxx::__ops::_Iter_comp_iter<bool (WordEntry<std::__cxx11::basic_string<char> >::*)(std::pair<std::__cxx11::basic_string<char>, int>&, std::pair<std::__cxx11::basic_string<char>, int>&)>]'
c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\bits\stl_algo.h:1882:25:   required from 'void std::__final_insertion_sort(_RandomAccessIterator, _RandomAccessIterator, _Compare) [with _RandomAccessIterator = __gnu_cxx::__normal_iterator<std::pair<std::__cxx11::basic_string<char>, int>*, std::vector<std::pair<std::__cxx11::basic_string<char>, int> > >; _Compare = __gnu_cxx::__ops::_Iter_comp_iter<bool (WordEntry<std::__cxx11::basic_string<char> >::*)(std::pair<std::__cxx11::basic_string<char>, int>&, std::pair<std::__cxx11::basic_string<char>, int>&)>]'
c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\bits\stl_algo.h:1968:31:   required from 'void std::__sort(_RandomAccessIterator, _RandomAccessIterator, _Compare) [with _RandomAccessIterator = __gnu_cxx::__normal_iterator<std::pair<std::__cxx11::basic_string<char>, int>*, std::vector<std::pair<std::__cxx11::basic_string<char>, int> > >; _Compare = __gnu_cxx::__ops::_Iter_comp_iter<bool (WordEntry<std::__cxx11::basic_string<char> >::*)(std::pair<std::__cxx11::basic_string<char>, int>&, std::pair<std::__cxx11::basic_string<char>, int>&)>]'
c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\bits\stl_algo.h:4739:18:   required from 'void std::sort(_RAIter, _RAIter, _Compare) [with _RAIter = __gnu_cxx::__normal_iterator<std::pair<std::__cxx11::basic_string<char>, int>*, std::vector<std::pair<std::__cxx11::basic_string<char>, int> > >; _Compare = bool (WordEntry<std::__cxx11::basic_string<char> >::*)(std::pair<std::__cxx11::basic_string<char>, int>&, std::pair<std::__cxx11::basic_string<char>, int>&)]'
wordentry.h:62:9:   required from 'void WordEntry<T>::getBot5() [with T = std::__cxx11::basic_string<char>]'
driver.cpp:34:19:   required from here
c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\bits\predefined_ops.h:123:18: error: must use '.*' or '->*' to call pointer-to-member function in '((__gnu_cxx::__ops::_Iter_comp_iter<bool (WordEntry<std::__cxx11::basic_string<char> >::*)(std::pair<std::__cxx11::basic_string<char>, int>&, std::pair<std::__cxx11::basic_string<char>, int>&)>*)this)->__gnu_cxx::__ops::_Iter_comp_iter<bool (WordEntry<std::__cxx11::basic_string<char> >::*)(std::pair<std::__cxx11::basic_string<char>, int>&, std::pair<std::__cxx11::basic_string<char>, int>&)>::_M_comp (...)', e.g. '(... ->* ((__gnu_cxx::__ops::_Iter_comp_iter<bool (WordEntry<std::__cxx11::basic_string<char> >::*)(std::pair<std::__cxx11::basic_string<char>, int>&, std::pair<std::__cxx11::basic_string<char>, int>&)>*)this)->__gnu_cxx::__ops::_Iter_comp_iter<bool (WordEntry<std::__cxx11::basic_string<char> >::*)(std::pair<std::__cxx11::basic_string<char>, int>&, std::pair<std::__cxx11::basic_string<char>, int>&)>::_M_comp) (...)'
         { return bool(_M_comp(*__it1, *__it2)); }
                  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\bits\predefined_ops.h: In instantiation of 
'bool __gnu_cxx::__ops::_Iter_comp_val<_Compare>::operator()(_Iterator, _Value&) [with _Iterator = __gnu_cxx::__normal_iterator<std::pair<std::__cxx11::basic_string<char>, 
int>*, std::vector<std::pair<std::__cxx11::basic_string<char>, int> > >; _Value = std::pair<std::__cxx11::basic_string<char>, int>; _Compare = bool (WordEntry<std::__cxx11::basic_string<char> >::*)(std::pair<std::__cxx11::basic_string<char>, int>&, std::pair<std::__cxx11::basic_string<char>, int>&)]':
c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\bits\stl_heap.h:129:48:   required from 'void std::__push_heap(_RandomAccessIterator, _Distance, _Distance, _Tp, _Compare) [with 
_RandomAccessIterator = __gnu_cxx::__normal_iterator<std::pair<std::__cxx11::basic_string<char>, int>*, std::vector<std::pair<std::__cxx11::basic_string<char>, int> > >; _Distance = int; _Tp = std::pair<std::__cxx11::basic_string<char>, int>; _Compare = __gnu_cxx::__ops::_Iter_comp_val<bool (WordEntry<std::__cxx11::basic_string<char> >::*)(std::pair<std::__cxx11::basic_string<char>, int>&, std::pair<std::__cxx11::basic_string<char>, int>&)>]'
c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\bits\stl_heap.h:230:23:   required from 'void std::__adjust_heap(_RandomAccessIterator, _Distance, _Distance, _Tp, _Compare) [with _RandomAccessIterator = __gnu_cxx::__normal_iterator<std::pair<std::__cxx11::basic_string<char>, int>*, std::vector<std::pair<std::__cxx11::basic_string<char>, int> > >; 
_Distance = int; _Tp = std::pair<std::__cxx11::basic_string<char>, int>; _Compare = __gnu_cxx::__ops::_Iter_comp_iter<bool (WordEntry<std::__cxx11::basic_string<char> >::*)(std::pair<std::__cxx11::basic_string<char>, int>&, std::pair<std::__cxx11::basic_string<char>, int>&)>]'
c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\bits\stl_heap.h:335:22:   required from 'void std::__make_heap(_RandomAccessIterator, _RandomAccessIterator, _Compare) [with _RandomAccessIterator = __gnu_cxx::__normal_iterator<std::pair<std::__cxx11::basic_string<char>, int>*, std::vector<std::pair<std::__cxx11::basic_string<char>, int> > >; _Compare = __gnu_cxx::__ops::_Iter_comp_iter<bool (WordEntry<std::__cxx11::basic_string<char> >::*)(std::pair<std::__cxx11::basic_string<char>, int>&, std::pair<std::__cxx11::basic_string<char>, int>&)>]'
c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\bits\stl_algo.h:1669:23:   required from 'void std::__heap_select(_RandomAccessIterator, _RandomAccessIterator, _RandomAccessIterator, _Compare) [with _RandomAccessIterator = __gnu_cxx::__normal_iterator<std::pair<std::__cxx11::basic_string<char>, int>*, std::vector<std::pair<std::__cxx11::basic_string<char>, int> > >; _Compare = __gnu_cxx::__ops::_Iter_comp_iter<bool (WordEntry<std::__cxx11::basic_string<char> >::*)(std::pair<std::__cxx11::basic_string<char>, int>&, std::pair<std::__cxx11::basic_string<char>, int>&)>]'
c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\bits\stl_algo.h:1930:25:   required from 'void std::__partial_sort(_RandomAccessIterator, _RandomAccessIterator, _RandomAccessIterator, _Compare) [with _RandomAccessIterator = __gnu_cxx::__normal_iterator<std::pair<std::__cxx11::basic_string<char>, int>*, std::vector<std::pair<std::__cxx11::basic_string<char>, int> > >; _Compare = __gnu_cxx::__ops::_Iter_comp_iter<bool (WordEntry<std::__cxx11::basic_string<char> >::*)(std::pair<std::__cxx11::basic_string<char>, int>&, 
std::pair<std::__cxx11::basic_string<char>, int>&)>]'
c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\bits\stl_algo.h:1945:27:   required from 'void std::__introsort_loop(_RandomAccessIterator, _RandomAccessIterator, _Size, _Compare) [with _RandomAccessIterator = __gnu_cxx::__normal_iterator<std::pair<std::__cxx11::basic_string<char>, int>*, std::vector<std::pair<std::__cxx11::basic_string<char>, int> > >; _Size = int; _Compare = __gnu_cxx::__ops::_Iter_comp_iter<bool (WordEntry<std::__cxx11::basic_string<char> >::*)(std::pair<std::__cxx11::basic_string<char>, int>&, std::pair<std::__cxx11::basic_string<char>, int>&)>]'
c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\bits\stl_algo.h:1965:25:   required from 'void std::__sort(_RandomAccessIterator, _RandomAccessIterator, _Compare) [with _RandomAccessIterator = __gnu_cxx::__normal_iterator<std::pair<std::__cxx11::basic_string<char>, int>*, std::vector<std::pair<std::__cxx11::basic_string<char>, int> > >; _Compare = __gnu_cxx::__ops::_Iter_comp_iter<bool (WordEntry<std::__cxx11::basic_string<char> >::*)(std::pair<std::__cxx11::basic_string<char>, int>&, std::pair<std::__cxx11::basic_string<char>, int>&)>]'
c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\bits\stl_algo.h:4739:18:   required from 'void std::sort(_RAIter, _RAIter, _Compare) [with _RAIter = __gnu_cxx::__normal_iterator<std::pair<std::__cxx11::basic_string<char>, int>*, std::vector<std::pair<std::__cxx11::basic_string<char>, int> > >; _Compare = bool (WordEntry<std::__cxx11::basic_string<char> >::*)(std::pair<std::__cxx11::basic_string<char>, int>&, std::pair<std::__cxx11::basic_string<char>, int>&)]'
wordentry.h:62:9:   required from 'void WordEntry<T>::getBot5() [with T = std::__cxx11::basic_string<char>]'
driver.cpp:34:19:   required from here
c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\bits\predefined_ops.h:144:11: error: must use '.*' or '->*' to call pointer-to-member function in '((__gnu_cxx::__ops::_Iter_comp_val<bool (WordEntry<std::__cxx11::basic_string<char> >::*)(std::pair<std::__cxx11::basic_string<char>, int>&, std::pair<std::__cxx11::basic_string<char>, int>&)>*)this)->__gnu_cxx::__ops::_Iter_comp_val<bool (WordEntry<std::__cxx11::basic_string<char> >::*)(std::pair<std::__cxx11::basic_string<char>, int>&, std::pair<std::__cxx11::basic_string<char>, int>&)>::_M_comp (...)', e.g. '(... ->* ((__gnu_cxx::__ops::_Iter_comp_val<bool (WordEntry<std::__cxx11::basic_string<char> >::*)(std::pair<std::__cxx11::basic_string<char>, int>&, std::pair<std::__cxx11::basic_string<char>, int>&)>*)this)->__gnu_cxx::__ops::_Iter_comp_val<bool (WordEntry<std::__cxx11::basic_string<char> >::*)(std::pair<std::__cxx11::basic_string<char>, int>&, std::pair<std::__cxx11::basic_string<char>, int>&)>::_M_comp) (...)'
  { return bool(_M_comp(*__it, __val)); }
           ^~~~~~~~~~~~~~~~~~~~~~~~~~~

c++

回答 2

Stack Overflow用户

回答已采纳

发布于 2021-05-02 01:10:33

你需要做一些不同的事情。

首先，您必须使比较器static如下所示：

template <class T>
class WordEntry
{
public:
//    int retrieveWordFreq(Node<T> *);
    void collectWords(T data);
    void getTop5();
    void getBot5();
    unordered_map<T, int> freqs;

private:
    int freq = 0;
   static bool sortByVal( pair<string, int> &a,  pair<string, int> &b); // static
};

因为普通成员函数指针比静态成员函数更复杂，因为它们需要一个对象来操作。

第二，你必须用它的限定名称来称呼它：

sort(vec.begin(), vec.end(), WordEntry<T>::sortByVal); // qualified name

票数 2

Stack Overflow用户

发布于 2021-05-02 03:48:39

可以在不对列表进行排序的情况下完成这一任务，并且运行速度要快得多，特别是对于大型列表。

要获得最大或最小的项，只需扫描一次列表并跟踪一个变量。如果您发现一个比当前最大的条目更大的条目，只需将其复制到最大的条目即可。如果您发现一个比当前最小项更小的条目，只需将其复制到最小项中即可。

给定一个大小为N的数组，下面的伪代码将找到最大或最小的。

Copy = array[0];

foreach Entry in array
  if searching for largest and Entry > Copy, set Copy = Entry
  if searching for smallest and Entry < Copy, set Copy = Entry

当此代码完成时，副本包含最大或最小的副本。此代码的运行时为O(n)，而排序第一，取最大或最小的运行时为O(n * lg(n))。

对于任何固定大小的K，只需复制一个大小为K的数组。伪代码的变化很小。

首先，我们假设存在一个函数Find_S_or_L_In_Copy()，该函数返回复制数组中最小或最大项的索引。

其次，我们使用这个函数来帮助跟踪最小或最大的K项。

foreach Slot in Copy
  Copy[Slot] = Array[0]

foreach Entry in Array
  if searching for largest K
    set Item = Find_S_or_L_In_Copy()
    if Entry > Copy[Item], set Copy[Item] = Entry

  if searching for smallest K
    set Item = Find_S_or_L_In_Copy()
    if Entry < Copy[Item], set Copy[Item] = Entry

当这些新代码退出时，数组Copy将包含来自Array的K最大或最小的条目。此代码的运行时为O(N * K)。

票数 0

页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持

原文链接：

https://stackoverflow.com/questions/67352068

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