如何根据python中的条件在列表中组合或保留字符串？

Question

我有三个清单:

li1 = ["a", "a", "a", "a", "b", "b", "a", "a", "b"]
li2 = ["a", "a", "a", "b", "a,", "b", "a", "a"]
li3 = ["b", "b", "a", "a", "b"]

我想通过"切片和粘贴"元素 "b"

结果应该是这样的:

li1 = ["aaaa", "b", "b", "aa", "b"]
li2 = ["aaa", "b", "a", "b", "aa"]
li3 = ["b", "b", "aa", "b"]

但我不知道如何处理这个...请帮助我!

Answer 1

使用itertools.groupby.

如果要加入不属于某个键的组

from itertools import groupby

def join_except_key(iterable, key='b'):
    groups = groupby(iterable)
    for k, group in groups:
        if k != key:
            yield ''.join(group) # more general: ''.join(map(str, group))
        else:
            yield from group

演示:

>>> li1 = ["a", "a", "a", "a", "b", "b", "a", "a", "b", "c", "c", "b", "c", "c"]
>>> list(join_except_key(li1))
['aaaa', 'b', 'b', 'aa', 'b', 'cc', 'b', 'cc']

如果要加入属于某个键的组

from itertools import groupby

def join_by_key(iterable, key='a'):
    groups = groupby(iterable)
    for k, group in groups:
        if k == key:
            yield ''.join(group) # more general: ''.join(map(str, group))
        else:
            yield from group

演示:

>>> li1 = ["a", "a", "a", "a", "b", "b", "a", "a", "b", "c", "c", "b", "c", "c"]
>>> list(join_by_key(li1))
['aaaa', 'b', 'b', 'aa', 'b', 'c', 'c', 'b', 'c', 'c']

什么groupby产生的细节(非发电机方法join_except_key)

>>> li1 = ["a", "a", "a", "a", "b", "b", "a", "a", "b", "c", "c", "b", "c", "c"]
>>> groups = [(k, list(group)) for k, group in groupby(li1)]
>>> groups
[('a', ['a', 'a', 'a', 'a']),
 ('b', ['b', 'b']),
 ('a', ['a', 'a']),
 ('b', ['b']),
 ('c', ['c', 'c']),
 ('b', ['b']),
 ('c', ['c', 'c'])]
>>>
>>> result = []
>>> for k, group in groups:
...:    if k != 'b':
...:        result.append(''.join(group))
...:    else:
...:        result.extend(group)
...:
>>> result
['aaaa', 'b', 'b', 'aa', 'b', 'cc', 'b', 'cc']

groups = [...第二行中的列表理解仅用于检查分组操作的元素,它只是正常工作groups = groupby(li1).