'Return most common top_n word features.
:param words: a list of words/tokens.
:param top_n: number of best words/tokens to use, sorted by frequency.
:rtype: list(str)
:return: A list of `top_n` words/tokens (with no duplicates) sorted by
frequency.'

def unigram_word_feats(self, words, top_n=None, min_freq=0):

    unigram_feats_freqs = FreqDist((word for word in words))
    return [w for (w, f) in unigram_feats_freqs.most_common(top_n) if (unigram_feats_freqs[w] > min_freq)]
