python - Python Beginner - 如何从另一个列表生成列表和频率

Question

鉴于：

[['x','a'], ['y','b'], ['z','a']]

我想要一个元素列表和第二个元素的计数频率：

[['x','a',2], ['y','b',1], ['z','a',2]]

Answer 1

>>> from collections import Counter
>>> L = [['x','a'], ['y','b'], ['z','a']]
>>> freq = Counter(y for x, y in L)
>>> [[x, y, freq[y]] for x, y in L]
[['x', 'a', 2], ['y', 'b', 1], ['z', 'a', 2]]

Answer 2

像往常一样，collections.Counter来救援。

你可以这样做：

from collections import Counter
pairs = [['x','a'], ['y','b'], ['z','a']]
counts = Counter(b for a,b in pairs)
pairs_with_counts = [[a, b, counts[b]] for a,b in pairs]

Answer 3

使用字典的替代解决方案：

mylist = [['x','a'], ['y','b'], ['z','a']]
d = {}
for (a, b) in mylist:
    try:
        d[b] += 1
    except KeyError:
        d[b] = 1

mynewlist = [[a, b, d[b]] for (a, b) in mylist]
print(mynewlist)

输出是[['x', 'a', 2], ['y', 'b', 1], ['z', 'a', 2]]