C++：使用地圖來排序和打印文本文件中字符串出現的值

Question

好吧，我試圖教自己如何使用地圖。我的意圖是打開一個txt文件並計算所有這些單詞，然後顯示特定單詞出現的次數。然後（如果它可能）我想在第二張地圖中使用第一張地圖來調用這些值，並只輸出出現的前10位（或20位或任何）頻繁詞並打印次數（從最大到最小）它與真實的單詞一起出現。

我已經想出瞭如何輸出所有單詞以及它們出現的次數。我認爲地圖已經很好地排列了我自動調用的實際字符串。我的問題是，我需要這些值排序，而不是字符串。

我已經對代碼的特定功能發表了評論，但我不確定這個其他地圖。

我只是尋求不同的想法。請不要吝嗇。

**有人向我提到了priority_queue，但這對我來說也是新的。如果你可以用一個更加口頭的方式來解釋這個例子，這樣我就可以理解，那會很棒！

#include <iostream> 
#include <map> 
#include <fstream> 
#include <string> 

using namespace std; 

//makes word count a declaration 
//makes count word a declaration 
typedef map <string, int> word_count; 
typedef map <int, string> count_word; 


int main() 
{ 
word_count word_count; 
string filename; 


// Get the filename. 
cout << "enter data.txt "; 
cin >> filename; 

// Open file. 
ifstream file(filename.c_str()); 

// Read in all the words. 
string word; 
while (file >> word) 
{ 
    // Remove punctuation. 
    int index; 
    while ((index = word.find_first_of(".,!?\\;-*+[]<>() '")) != string::npos) 
    { 
     word.erase(index, 1); 
    } 

    ++word_count[word]; 
} 


std::map <int, string> count_word; 

// Print out the first 10 words counts. 
word_count::const_iterator current(word_count.begin()); 


int count = 0; 
while (current != word_count.end() && count<10) 
{ 

    count++; 
    cout << "The word '" << current->first << "'  appears " << current->second << " times" << endl; 
    count_word.insert(std::pair<int, string>(current->second, current->first)); 
    ++current; 

} 


count_word::const_iterator new_current(count_word.begin()); 
count = 0; 

while (new_current != count_word.end() && count<10) 
{ 

    count++; 
    cout << new_current -> first << " times appears the word '" << 
      current -> second << endl; 
    ++new_current; 
} 

system("pause"); 
    } 

Answer 1

您可以創建一個新的地圖容器如下

std:map<int,string> count_word 

，並從現有地圖這一插入對。新地圖會自行排序。

這裏的代碼片斷我沒有編譯。

std:map<int,string> count_word; 
word_count::const_iterator current(word_count.begin()); 


int count = 0; 
while (current != word_count.end() && count<10) 
{ 

    count++; 
    cout << "The word '" << current -> first << "'  appears " << current -> second << " times" << endl; 
    count_word.insert(std::pair<int,string>(current->second,current->first); 
    ++current; 

} 

count_word::const_iterator new_current(count_word.begin()); 
//for(auto &x:count_word) 
//std::cout<<x->first<<"no of times"<< x->second << "word"<<endl; 
//Either you can use above 2 line to print or below given few lines 
while (new_current != word_count.end() && count<10) 
{ 

    count++; 
    cout << new_current -> first << " times appears the word '" <<<< current -> second << endl; 
    ++new_current; 
} 

Answer 2

一個priority queue允許設置，你可以使用你的優勢自定義的比較，通過比較計數（映射值）您的隊列可以通過值進行排序（map也可以用一個比較，但它僅適用於鍵）：

typedef pair<string,int> str_to_int; // = word_count::value_type 
struct Compare { 
    bool operator()(const str_to_int & a, const str_to_int & b) { 
     return a.second < b.second; 
    } 
}; 
// ... 
priority_queue<str_to_int, vector<str_to_int>, Compare> queue(word_count.begin(), word_count.end()); 
// Print the top 10 
for (int i=0; i<10; ++i) { 
    const str_to_int & e = queue.top(); 
    queue.pop(); 
    cout << "The word '" << e.first << "'  appears " << e.second << " times" << endl; 
}