Python初学者-如何从另一个列表生成列表和频率

鉴于：

我想要一个元素列表和第二个元素的计数频率：

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

像往常一样，他来营救

你可以这样做：

>>> 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]]

---

另一种解决方案是使用字典：

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]

---

输出是

[['x'，'a'，2'，'y'，'b'，1'，'z'，'a'，2]

我建议不要使用小写的

l

作为变量名，它可能会与

1

计数器是一个字典混淆。这一切都是在幕后进行的，只是速度要快得多

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]

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)