C++: How to Count the Frequency of the Elements in a Container

C++: コンテナ中の要素の出現頻度をカウントする

 

コード

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56

#include <iostream> #include <vector> #include <map> #include <algorithm>   template <class InputIterator> std::vector<std::pair<typename InputIterator::value_type, int> > frequency(InputIterator first, InputIterator last) {   typedef typename InputIterator::value_type ValType;   typedef std::map<ValType, int> MapType;   typedef std::vector<std::pair<ValType, int> > VecType;     MapType m;   for (InputIterator it = first; it != last; ++it) {     if (m.find(*it) == m.end()) {       m.insert(typename MapType::value_type(*it, 1));     } else {       ++m[*it];     }   }     return VecType(m.begin(), m.end()); }   // for utility template <typename T> std::ostream & operator<<(std::ostream & stream, std::vector<T> & v) {   stream << "[";   for (typeof(v.begin()) i = v.begin(); i != v.end(); ++i) {     if (i != v.begin()) { stream << ", "; }     stream << *i;   }   stream << "]";   return stream; } template <typename T, typename U> std::ostream & operator<<(std::ostream & stream, std::pair<T, U> & p) {   stream << "(" << p.first << ", " << p.second << ")";   return stream; } #define print(a) std::cout << a << std::endl #define all(a) (a).begin(),(a).end()   // main using namespace std;   int main(int argc, char **argv) {   string apple = "apple";   vector<pair<char, int> > a = frequency(all(apple));   print(apple << ": " << a);     int xs[] = { 1, 3, 5, 4, 3, 2 };   vector<int> v(xs, xs + sizeof(xs) / sizeof(xs[0]));   vector<pair<int, int> > b = frequency(all(v));   print(v << ": " << b); }

 

出力例

1 2	apple: [(a, 1), (e, 1), (l, 1), (p, 2)] [1, 3, 5, 4, 3, 2]: [(1, 1), (2, 1), (3, 2), (4, 1), (5, 1)]

やはり、Scalaとかに比べるとストレスフルだなあ。