vectorize function

function vectorize(text: string, vocab: Map<string, number>): Float32Array {
  const v = new Float32Array(vocab.size);
  for (const ng of charNgrams(text)) {
    const idx = vocab.get(ng);
    if (idx !== undefined) v[idx] += 1;
  }
  let norm = 0;
  for (let i = 0; i < v.length; i++) norm += v[i] * v[i];
  norm = Math.sqrt(norm);
  if (norm > 0) for (let i = 0; i < v.length; i++) v[i] /= norm;
  return v;
}