from typing import Counter


def get_unique_characters(rows, min_count=2):
    """Given a bunch of text rows, get all unique chars that occur in it."""
    def char_iterator():
        for row in rows.values:
            for char in row:
                yield str(char).lower()

    return [
        c for c, count
        in Counter(char_iterator()).items()
        if count >= min_count
    ]