Remove from gold and pred all items with labels designated to ignore.

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