word frequency tool

freqs.cpp

// compile with g++ --std=c++11
// g++ --std=c++11 freqs.cpp -o freqs

#include <iostream>
#include <sstream>
#include <fstream>
#include <regex>

#include <algorithm>
#include <map>
#include <vector>


using namespace std;

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

    locale::global(locale(""));
    regex word_pattern("[[:alpha:]]+");

    map<string, int> frequency_map;

    ifstream input_file (argv[1]);
    ofstream out_file (argv[2]);

    string line;

    if (input_file.is_open())
    {
        while (getline(input_file, line)) {

            //remove punctuation;
            line.erase(remove_if(line.begin(), line.end(), ::ispunct), line.end());
            istringstream iss(line);
            while(iss)
            {
                string sub_str;
                iss >> sub_str;
                if (regex_match(sub_str, word_pattern))
                {
                    //convert word to lower case;
                    transform(sub_str.begin(), sub_str.end(), sub_str.begin(), ::tolower);
                    map<string, int>::iterator it = frequency_map.find(sub_str);

                    if (it != frequency_map.end()) {
                        frequency_map[sub_str] += 1;
                    }
                    else {
                        frequency_map[sub_str] = 1;
                    }

                }
            }
        }
        input_file.close();
    }
    else {
        cout << "Unable to open input file" << endl;
    }

    map<string, int>::iterator it;
    vector<pair<int, string>> frequency_list;
    //build list of pairs
    for (it = frequency_map.begin(); it != frequency_map.end(); it++) {
        frequency_list.push_back(make_pair(-it -> second, it -> first));
    }
    //sort pairs
    sort(frequency_list.begin(), frequency_list.end());
    if (out_file.is_open()) {
        for (auto &item: frequency_list) {
            out_file << abs(item.first) << " " << item.second << endl;
        }
    } else {
        cout << "Unable to open out file" << endl;
    }
    out_file.close();

    return 0;
}