用Python在嵌套列表中查询计数频率

Question

我有这样一个清单：

dttrain = [["sunny","hot","high","false","no"],
    ["sunny","hot","high","true","no"],
    ["overcast","hot","high","false","yes"]]

我想按最后一个索引计算频率，例如：

^{pr2}$

我尝试了我自己的代码：

c = Counter(x for sublist in dttrain for x in sublist)

但这表明：

Counter({'yes': 9, 'false': 8, 'high': 7, 'normal': 7, 'true': 6, 'mild': 6, 'sunny': 5, 'no': 5, 'rainy': 5, 'hot': 4,'overcast': 4, 'cool': 4})

Answer 1

使用itertools(product and chain)和collections.Counter的组合

from itertools import product, chain
from collections import Counter
{' '.join(k):v for k,v in Counter(chain(*[product(i[:2],[i[-1]]) for i in dttrain])).items()}

输出：

^{pr2}$

Answer 2

下面是一些杂乱的代码：

def iterate_key(name, _counter):
    """
    Iterate a key in a dict, create key if it doesn't exist.

    :param str name: Name of key to iterate.
    :param dict[int] _counter: Dictionary storing count data.
    :return: _counter after iterating key.
    """
    if name not in counter:
        _counter[name] = 1
    else:
        _counter[name] += 1
    return _counter


counter = {}
for sub_list in dttrain:
    key_name = '{}_{}'.format(sub_list[0], sub_list[-1])
    counter = iterate_key(key_name, counter)

    key_name = '{}_{}'.format(sub_list[1], sub_list[-1])
    counter = iterate_key(key_name, counter)

print(counter)