regexWordStatistic.cpp

#include <algorithm>
#include <cstdlib>
#include <fstream>
#include <iostream>
#include <regex>
#include <string>
#include <map>
#include <unordered_map>
#include <utility>

using str2Int = std::unordered_map<std::string, std::size_t>;          
using intAndWords = std::pair<std::size_t, std::vector<std::string>>;
using int2Words= std::map<std::size_t,std::vector<std::string>>; 


// count the frequency of each word
str2Int wordCount(const std::string &text) {
  std::regex wordReg(R"(\w+)");                                        
  std::sregex_iterator wordItBegin(text.begin(), text.end(), wordReg); 
  const std::sregex_iterator wordItEnd;
  str2Int allWords;
  for (; wordItBegin != wordItEnd; ++wordItBegin) {
    ++allWords[wordItBegin->str()];
  }
  return allWords;
}

// get to each frequency the words
int2Words frequencyOfWords(str2Int &wordCount) {
  int2Words freq2Words;
  for (auto wordIt : wordCount) {
    auto freqWord = wordIt.second;
    if (freq2Words.find(freqWord) == freq2Words.end()) {
      freq2Words.insert(intAndWords(freqWord, {wordIt.first}));
    } else {
      freq2Words[freqWord].push_back(wordIt.first);
    }
  }
  return freq2Words;
}

int main(int argc, char *argv[]) {

  std::cout << '\n';

  // get the filename
  std::string myFile;
  if (argc == 2) {
    myFile = {argv[1]};
  } else {
    std::cerr << "Filename missing !" << '\n';
    exit(EXIT_FAILURE);
  }

  // open the file
  std::ifstream file(myFile, std::ios::in);
  if (!file) {
    std::cerr << "Can't open file " + myFile + "!" << '\n';
    exit(EXIT_FAILURE);
  }

  // read the file
  std::stringstream buffer;
  buffer << file.rdbuf();
  std::string text(buffer.str());

  // get the frequency of each word
  auto allWords = wordCount(text);                                     

  std::cout << "The first 20 (key, value)-pairs: " << '\n';
  auto end = allWords.begin();
  std::advance(end, 20);
  for (auto pair = allWords.begin(); pair != end; ++pair) {            
    std::cout << "(" << pair->first << ": " << pair->second << ")";
  }
  std::cout << "\n\n";

  std::cout << "allWords[Web]: " << allWords["Web"] << '\n';      
  std::cout << "allWords[The]: " << allWords["The"] << "\n\n";

  std::cout << "Number of unique words: ";
  std::cout << allWords.size() << "\n\n";                              

  size_t sumWords = 0;
  for (auto wordIt : allWords)
    sumWords += wordIt.second;
  std::cout << "Total number of words: " << sumWords << "\n\n";

  auto allFreq = frequencyOfWords(allWords);                           


  std::cout << "Number of different frequencies: " << allFreq.size() << "\n\n";

  std::cout << "All frequencies: ";                                    
  for (auto freqIt : allFreq)
    std::cout << freqIt.first << " ";
  std::cout << "\n\n";

  std::cout << "The most frequently used word(s): " << '\n';      
  auto atTheEnd = allFreq.rbegin();
  std::cout << atTheEnd->first << " :";
  for (auto word : atTheEnd->second)
    std::cout << word << " ";
  std::cout << "\n\n";

  std::cout << "All words which appear more than 1000 times:" << '\n';
  auto biggerIt =
      std::find_if(allFreq.begin(), allFreq.end(),
                   [](intAndWords iAndW) { return iAndW.first > 1000; });
  if (biggerIt == allFreq.end()) {
    std::cerr << "No word appears more than 1000 times !" << '\n';
    exit(EXIT_FAILURE);
  } else {
    for (auto allFreqIt = biggerIt; allFreqIt != allFreq.end(); ++allFreqIt) {
      std::cout << allFreqIt->first << " :";
      for (auto word : allFreqIt->second)
        std::cout << word << " ";
      std::cout << '\n';
    }
  }
  std::cout << '\n';
  
}