def count_chunks(corpus,pos):
    """
    Computes the chunk distribution given a part of speach
    :param corpus:
    :param pos: part of speach
    :return: map from chunk to frequency of that chunk
    """
    freqMap = {}
    corpus = [val for sublist in corpus for val in sublist]
    for row in corpus:
        if row["pos"] == pos:
            chunk = row["chunk"]
            freqMap[chunk] = 1 + freqMap.get(chunk, 0) # one liner for increment, else set default 0
    return freqMap