chrome/browser/metrics/perf/random_selector.h

   1 // Copyright 2015 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #ifndef CHROME_BROWSER_METRICS_PERF_RANDOM_SELECTOR_H_
   6 #define CHROME_BROWSER_METRICS_PERF_RANDOM_SELECTOR_H_
   7
   8 #include <string>
   9 #include <vector>
  10
  11 #include "base/macros.h"
  12
  13 // RandomSelector can be used to pick vectors of strings according to certain
  14 // probabilities. The probabilities are set using SetOdds(). A randomly picked
  15 // vector can be obtained by calling Select().
  16 //
  17 // Sample usage:
  18 //
  19 // RandomSelector random_selector;
  20 // std::vector<RandomSelector::WeightAndValue> odds {
  21 //   {50, "a"},
  22 //   {40, "b"},
  23 //   {10, "c"}
  24 // };
  25 // random_selector.SetOdds(odds);
  26 //
  27 // std::vector<std::string>& selection = random_selector.Select();
  28 //
  29 // The above line should return "a" with a probability of 50%,
  30 // "b" with a probability of 40%, and "c" with a probability of 10%:
  31 class RandomSelector {
  32  public:
  33   struct WeightAndValue {
  34     WeightAndValue(double weight, const std::string& value)
  35       : weight(weight), value(value) {
  36     }
  37
  38     // Probability weight for selecting this value.
  39     double weight;
  40     // Value to be returned by Select(), if selected.
  41     std::string value;
  42   };
  43
  44   RandomSelector();
  45   virtual ~RandomSelector();
  46
  47   // Set the probabilities for various strings.
  48   void SetOdds(const std::vector<WeightAndValue>& odds);
  49
  50   // Randomly select one of the values from the set.
  51   const std::string& Select();
  52
  53   // Returns the number of string entries.
  54   size_t num_values() const {
  55     return odds_.size();
  56   }
  57
  58   // Sum of the |weight| fields in the vector.
  59   static double SumWeights(const std::vector<WeightAndValue>& odds);
  60
  61  private:
  62   // Get a floating point number between 0.0 and |max|.
  63   virtual double RandDoubleUpTo(double max);
  64
  65   // Get a string corresponding to |random| that is in the odds vector.
  66   // |random| must be a number between zero and the sum of the probability
  67   // weights.
  68   const std::string& GetValueFor(double random);
  69
  70   // A dictionary representing the strings to choose from and associated odds.
  71   std::vector<WeightAndValue> odds_;
  72
  73   // Sum of the probability weights.
  74   double sum_of_weights_;
  75
  76   DISALLOW_COPY_AND_ASSIGN(RandomSelector);
  77 };
  78
  79 #endif  // CHROME_BROWSER_METRICS_PERF_RANDOM_SELECTOR_H_