Compute ranks

ranks.js

const ranks = (values, comparator = (a, b) => b - a) => values
  .map((value, i) => [value, i])
  .slice().sort(([a], [b]) => comparator(a, b))
  .reduce((ranks, [value, i], rank, ordered) => [
     ...ranks.slice(0, i),
     rank && !comparator(value, ordered[rank - 1][0]) ? ranks[ordered[rank - 1][1]] : rank + 1,
     ...ranks.slice(i + 1),
  ], Array.from({length: values.length}))