function mode(values, f) {
  const m = new InternMap();
  let greatest;
  let greatestCount = 0;
  for (const v of Array.from(values, f)) {
    const count = (m.get(v) || 0) + 1;
    if (count > greatestCount) greatestCount = count, greatest = v;
    m.set(v, count);
  }
  return greatest;
}