Sample apps with click data first.

When choosing the apps to send as negative examples,
prefer to send data from apps that have already been
clicked on. These will have data more useful for
training.

Bug: 899123
Change-Id: I79973f0ca67fe8f6104dae5850125726bae0567d
Reviewed-on: https://chromium-review.googlesource.com/c/1491151Reviewed-by: Jia Meng <jiameng@chromium.org>
Commit-Queue: Paul Dyson <pdyson@chromium.org>
Cr-Commit-Position: refs/heads/master@{#636587}

chrome/browser/ui/app_list/app_launch_event_logger.cc

@@ -41,7 +41,7 @@ const char AppLaunchEventLogger::kShouldSync[] = "should_sync";
 
 namespace {
 
-constexpr int kNumRandomAppsToLog = 5;
+constexpr unsigned int kNumRandomAppsToLog = 5;
 const char kArcScheme[] = "arc://";
 const char kExtensionSchemeWithDelimiter[] = "chrome-extension://";
 
@@ -75,6 +75,26 @@ int ExponentialBucket(int value, float base) {
   return round(pow(base, round(log(value) / log(base))));
 }
 
+// Selects a random sample of size |sample_size| from |population|.
+std::vector<std::string> Sample(const std::vector<std::string>& population,
+                                unsigned int sample_size) {
+  std::vector<std::string> sample;
+  unsigned int index = 0;
+  // Reservoir sampling.
+  for (const std::string& candidate : population) {
+    if (index < sample_size) {
+      sample.push_back(candidate);
+    } else {
+      const uint64_t r = base::RandGenerator(index + 1);
+      if (r < sample_size) {
+        sample[r] = candidate;
+      }
+    }
+    index++;
+  }
+  return sample;
+}
+
 int HourOfDay(base::Time time) {
   base::Time::Exploded exploded;
   time.LocalExplode(&exploded);
@@ -329,26 +349,28 @@ ukm::SourceId AppLaunchEventLogger::GetSourceId(
 
 std::vector<std::string> AppLaunchEventLogger::ChooseAppsToLog(
     const std::string clicked_app_id) {
-  int index = 0;
   bool has_clicked_app = false;
-  std::vector<std::string> apps;
-
-  // Reservoir sampling, but must also include clicked_app_id if it is
-  // present.
+  std::vector<std::string> clicked_apps;
+  std::vector<std::string> unclicked_apps;
+  // Group apps by whether they have been clicked on. Do not include the
+  // currently clicked app.
   for (auto& app : app_features_map_) {
     if (app.first == clicked_app_id) {
       has_clicked_app = true;
       continue;
     }
-    if (index < kNumRandomAppsToLog) {
-      apps.push_back(app.first);
+    if (app.second.has_most_recently_used_index()) {
+      clicked_apps.push_back(app.first);
     } else {
-      const uint64_t r = base::RandGenerator(index + 1);
-      if (r < kNumRandomAppsToLog) {
-        apps[r] = app.first;
-      }
+      unclicked_apps.push_back(app.first);
     }
-    index++;
+  }
+
+  std::vector<std::string> apps(Sample(clicked_apps, kNumRandomAppsToLog));
+  if (apps.size() < kNumRandomAppsToLog) {
+    std::vector<std::string> unclicked_sample(
+        Sample(unclicked_apps, kNumRandomAppsToLog - apps.size()));
+    apps.insert(apps.end(), unclicked_sample.begin(), unclicked_sample.end());
   }
   if (has_clicked_app) {
     apps.push_back(clicked_app_id);
@@ -480,8 +502,8 @@ void AppLaunchEventLogger::Log(AppLaunchEvent app_launch_event) {
                                        kTotalHoursBucketSizeMultiplier))
       .Record(ukm::UkmRecorder::Get());
 
-  // Log click data about the app clicked on and up to five other apps chosen at
-  // random. This represents the state of the data immediately before the click.
+  // Log click data about the app clicked on and up to five other apps. This
+  // represents the state of the data immediately before the click.
   const std::vector<std::string> apps_to_log =
       ChooseAppsToLog(app_launch_event.app_id());
 

chrome/browser/ui/app_list/app_launch_event_logger.h

@@ -92,7 +92,12 @@ class AppLaunchEventLogger {
                             const std::string& app_id,
                             const std::string& arc_package_name,
                             const std::string& pwa_url);
-  // Randomly chooses up to five apps to log, plus the app clicked on.
+  // Chooses up to five apps to log, plus the app clicked on. Randomly chooses
+  // up to five apps that have previously been clicked on. These are preferred
+  // as they have metrics about past click behaviour. If there are fewer than
+  // five of these apps, then, in addition, randomly chooses from apps not
+  // clicked on, to get a total of five apps. If there are fewer than five apps
+  // that can be logged on the device, logs every app once.
   std::vector<std::string> ChooseAppsToLog(const std::string clicked_app_id);
   // Records a UMA histogram of the app type clicked on.
   void RecordAppTypeClicked(AppLaunchEvent_AppType app_type);