python - 满足列表列表中条件的元组中值的频率分布

Question

我有以下元组列表:

[[("AA","AA"),("QQ","")],[("CC",""),("QQ","")],...]

当元组的第二项是 "" 时，我想获取每个值作为元组的第一项出现的频率。

上面的例子是这样的:

{"QQ":2, "CC":1}

Answer 1

我会使用 collections.Counter + itertools.chain 来完成:

>>> data = [[("AA","AA"),("QQ","")],[("CC",""),("QQ","")]]
>>> from itertools import chain
>>> from collections import Counter
>>> Counter(left for left, right in chain.from_iterable(data) if not right)
Counter({'QQ': 2, 'CC': 1})

---

这是有效的，因为 Counter 计算它被喂食的东西:

>>> Counter(["QQ", "QQ", "AA", "CC"])
Counter({'QQ': 2, 'AA': 1, 'CC': 1})

itertools.chain.from_iterable 可用于扁平化数据:

>>> list(chain.from_iterable(data))
[('AA', 'AA'), ('QQ', ''), ('CC', ''), ('QQ', '')]

我们使用 genexp 只选择第二个为空的项(对于字符串可以简单地写成 if not somestring):

>>> list(left for left, right in chain.from_iterable(data) if not right)
['QQ', 'CC', 'QQ']