private DataSource downsample(DataSource data, LongSet testUsers) throws IOException {
String fileName = getFileName(data);
File output = new File(fileName);
UpToDateChecker checker = new UpToDateChecker();
checker.addInput(data.lastModified());
checker.addOutput(output);
if (!checker.isUpToDate()) {
RandomOrder<Rating> order = new RandomOrder<Rating>();
Random rng = new Random();
// write datasource
CSVWriter csv = null;
try {
csv = CSVWriter.open(output, null);
Cursor<UserHistory<Rating>> histories =
data.getUserEventDAO().streamEventsByUser(Rating.class);
for (UserHistory<Rating> ratings : histories) {
List<Rating> rats = new ArrayList<Rating>(ratings);
order.apply(rats, rng);
for (int i = 0; i < rats.size(); i++) {
if (!testUsers.contains(ratings.getUserId()) || i < retain) {
Rating rating = rats.get(i);
Preference pref = rating.getPreference();
csv.writeRow(
Lists.newArrayList(
rating.getUserId(),
rating.getItemId(),
rating.getValue(),
rating.getTimestamp()));
}
}
}
} finally {
if (csv != null) {
csv.close();
}
}
}
CSVDataSourceBuilder builder = new CSVDataSourceBuilder(data.getName());
builder.setDomain(data.getPreferenceDomain());
builder.setFile(output);
return builder.build();
}
