metrics: Add RandomSelector, a class that randomly selects items with odds

chrome/browser/metrics/random_selector.h

+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include <string>
+#include <vector>
+
+#ifndef CHROME_BROWSER_METRICS_RANDOM_SELECTOR_H_
+#define CHROME_BROWSER_METRICS_RANDOM_SELECTOR_H_
+
+namespace metrics {
+
+// RandomSelector can be used to pick vectors of strings according to certain
+// probabilities. The probabilities are set using SetOdds(). A randomly picked
+// vector can be obtained by calling GetNext().
+//
+// Sample usage:
+//
+// RandomSelector random_selector;
+// std::vector<RandomSelector::OddsAndValue> odds {
+//   {50, {"a"}},
+//   {40, {"b"}},
+//   {10, {"c"}}
+// };
+// random_selector.SetOdds(odds);
+//
+// // The following should return "a" with a probability of 50%,
+// // "b" with a probability of 40%, and "c" with a probability of 10%:
+//
+// std::vector<std::string>& selection = random_selector.GetNext();
+class RandomSelector {
+ public:
+  struct OddsAndValue {
+    template <size_t N>
+    OddsAndValue(double weight_, const char* (&array)[N])

[Alexei Svitkine (slow), 2015/09/11 21:00:54]

Nit: No _'s for params. I think using the same name as the field name should
work fine.

[dhsharp, 2015/09/11 22:53:25]

Oh, okay. Was thinking that wouldn't work. Done.

+      : weight(weight_), value(array, array + N) {
+    }
+
+    double weight;
+    std::vector<std::string> value;
+  };
+
+  RandomSelector();
+  virtual ~RandomSelector();
+
+  // Set the probabilities for various strings.
+  void SetOdds(const std::vector<OddsAndValue>& odds);
+
+  // Get the next randomly picked string in |next|.
+  const std::vector<std::string>& GetNext();
+
+  // Returns the number of string entries.
+  size_t GetNumValues() const {
+    return odds_.size();
+  }
+
+  // Sum of the |weight| fields in the vector.
+  static double SumOdds(const std::vector<OddsAndValue>& odds);
+
+ private:
+  // Get a floating point number between 0.0 and |max|.
+  virtual double RandDoubleUpTo(double max);
+
+  // Get a string corresponding to a random double |value| that is in our odds
+  // vector. Stores the result in |key|.
+  const std::vector<std::string>& GetKeyOf(double value);
+
+  // A dictionary representing the strings to choose from and associated odds.
+  std::vector<OddsAndValue> odds_;
+
+  double sum_of_odds_;
+};

[Alexei Svitkine (slow), 2015/09/11 21:00:54]

DISALLOW_COPY_AND_ASSIGN().

[dhsharp, 2015/09/11 22:53:25]

Done.

+
+}  // namespace metrics
+
+#endif  // CHROME_BROWSER_METRICS_RANDOM_SELECTOR_H_