如何编写一个带字符串的函数并按频率递减的顺序打印字母？

Question

我到目前为止:

def most_frequent(string):
    d = dict()
    for key in string:
        if key not in d:
            d[key] = 1
        else:
            d[key] += 1
    return d

print most_frequent('aabbbc')

返回:

{'a': 2, 'c': 1, 'b': 3}

现在我需要:

1. 扭转这一对
2. 按降序排序
3. 只打印出来的字母

我应该将此字典转换为元组还是列表？

Answer 1

这是一个单行答案

sortedLetters = sorted(d.iteritems(), key=lambda (k,v): (v,k))

Answer 2

这应该做得很好.

def frequency_analysis(string):
    d = dict()
    for key in string:
        d[key] = d.get(key, 0) + 1
    return d

def letters_in_order_of_frequency(string):
    frequencies = frequency_analysis(string)
    # frequencies is of bounded size because number of letters is bounded by the dictionary, not the input size 
    frequency_list = [(freq, letter) for (letter, freq) in frequencies.iteritems()]
    frequency_list.sort(reverse=True)
    return [letter for freq, letter in frequency_list]

string = 'aabbbc'
print letters_in_order_of_frequency(string)