问题描述

统计文件中每个英文"词出现频率的优雅有效方法有哪些?

What are the elegant and effective ways to count the frequency of each "english" word in a file?

推荐答案

首先，我定义了 letter_only std::locale 以便忽略来自流的标点符号，并仅从输入流中读取有效的英文"字母.这样，流会将词 "ways"、"ways." 和 "ways!" 视为同一个词 >"ways"，因为流将忽略诸如 "." 和 "!" 之类的标点符号.

First of all, I define letter_only std::locale so as to ignore punctuations coming from the stream, and to read only valid "english" letters from the input stream. That way, the stream will treat the words "ways", "ways." and "ways!" as just the same word "ways", because the stream will ignore punctuations like "." and "!".

struct letter_only: std::ctype<char> 
{
    letter_only(): std::ctype<char>(get_table()) {}

    static std::ctype_base::mask const* get_table()
    {
        static std::vector<std::ctype_base::mask> 
            rc(std::ctype<char>::table_size,std::ctype_base::space);

        std::fill(&rc['A'], &rc['z'+1], std::ctype_base::alpha);
        return &rc[0];
    }
};

解决方案 1

int main()
{
     std::map<std::string, int> wordCount;
     ifstream input;
     input.imbue(std::locale(std::locale(), new letter_only())); //enable reading only letters!
     input.open("filename.txt");
     std::string word;
     while(input >> word)
     {
         ++wordCount[word];
     }
     for (std::map<std::string, int>::iterator it = wordCount.begin(); it != wordCount.end(); ++it)
     {
           cout << it->first <<" : "<< it->second << endl;
     }
}

<小时>

解决方案 2

struct Counter
{
    std::map<std::string, int> wordCount;
    void operator()(const std::string & item) { ++wordCount[item]; }
    operator std::map<std::string, int>() { return wordCount; }
};

int main()
{
     ifstream input;
     input.imbue(std::locale(std::locale(), new letter_only())); //enable reading only letters!
     input.open("filename.txt");
     istream_iterator<string> start(input);
     istream_iterator<string> end;
     std::map<std::string, int> wordCount = std::for_each(start, end, Counter());
     for (std::map<std::string, int>::iterator it = wordCount.begin(); it != wordCount.end(); ++it)
     {
          cout << it->first <<" : "<< it->second << endl;
     }
 }

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