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  1. #include <iostream>
  2. #include <map>
  3. #include <vector>
  4.  
  5. typedef std::vector<std::vector<double> > matrix_t;
  6. struct stats {
  7.     int count = 0;
  8.     double total = 0.0;
  9. };
  10. typedef std::map<double, stats> results_t;
  11.  
  12. results_t aggregate(matrix_t const& matrix)
  13. {
  14.     results_t results;
  15.     for (auto const& row: matrix)
  16.     {
  17.         auto const& id = row[0];
  18.         auto const& value = row[1];
  19.         auto& stats = results[id];
  20.         ++stats.count;
  21.         stats.total += value;
  22.     }
  23.  
  24.     return results;
  25. }
  26.  
  27. int main()
  28. {
  29.     matrix_t matrix = {
  30.         {1, 10},
  31.         {2, 20},
  32.         {1, 30},
  33.         {2, 40},
  34.         {3, 60}
  35.     };
  36.  
  37.     std::cout << "ID" << "\tCOUNT" << "\tMEAN" << std::endl;
  38.     for (auto const& row: aggregate(matrix))
  39.     {
  40.         auto stats = row.second;
  41.         std::cout << row.first << '\t' << stats.count << '\t' << stats.total / stats.count << std::endl;
  42.     }
  43. }
Success #stdin #stdout 0s 3476KB
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stdin
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Standard input is empty
stdout
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ID	COUNT	MEAN
1	2	20
2	2	30
3	1	60
https://ideone.com/pNf5OD
language:
C++14 (gcc 8.3)
created:
11 years ago
visibility:
public

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