docs: def _drop_ignored(gold, pred, ignore_in_gold, ignore_in_pred):
      """Remove from gold and pred all items with labels designated to ignore."""
      keepers = np.ones_like(gold).astype(bool)
      for x in ignore_in_gold:
          keepers *= np.where(gold != x, 1, 0).astype(bool)
      for x in ignore_in_pred:
          keepers *= np.where(pred != x, 1, 0).astype(bool)
  
      gold = gold[keepers]
      pred = pred[keepers]
      return gold, pred