找到Python列表中最常见元素的有效方法是什么?

我的列表项可能不是可哈希的,所以不能使用字典。 同样,在抽取的情况下,应返回索引最低的项。例子:

>>> most_common(['duck', 'duck', 'goose'])
'duck'
>>> most_common(['goose', 'duck', 'duck', 'goose'])
'goose'

当前回答

从这里借鉴,这可以在Python 2.7中使用:

from collections import Counter

def Most_Common(lst):
    data = Counter(lst)
    return data.most_common(1)[0][0]

比Alex的解决方案快4-6倍,比newacct提出的一行程序快50倍。

在CPython 3.6+(任何Python 3.7+)上,上面将选择第一个看到的元素。如果你在旧的Python上运行,为了检索列表中第一个出现的元素,你需要进行两次传递来保持顺序:

# Only needed pre-3.6!
def most_common(lst):
    data = Counter(lst)
    return max(lst, key=data.get)

其他回答

>>> li  = ['goose', 'duck', 'duck']

>>> def foo(li):
         st = set(li)
         mx = -1
         for each in st:
             temp = li.count(each):
             if mx < temp:
                 mx = temp 
                 h = each 
         return h

>>> foo(li)
'duck'

这是一个很简单的解,时间复杂度是线性的

L =['鹅','鸭','鸭']

def most_common (L):

current_winner = 0
max_repeated = None
for i in L:
    amount_times = L.count(i)
    if amount_times > current_winner:
        current_winner = amount_times
        max_repeated = i

return max_repeated

打印(most_common (L)

“鸭子”

number是列表中重复次数最多的元素吗

如果它们是不可哈希的,您可以对它们进行排序,并对结果进行一次循环,以计数项(相同的项将彼此相邻)。但是使它们可哈希并使用字典可能更快。

def most_common(lst):
    cur_length = 0
    max_length = 0
    cur_i = 0
    max_i = 0
    cur_item = None
    max_item = None
    for i, item in sorted(enumerate(lst), key=lambda x: x[1]):
        if cur_item is None or cur_item != item:
            if cur_length > max_length or (cur_length == max_length and cur_i < max_i):
                max_length = cur_length
                max_i = cur_i
                max_item = cur_item
            cur_length = 1
            cur_i = i
            cur_item = item
        else:
            cur_length += 1
    if cur_length > max_length or (cur_length == max_length and cur_i < max_i):
        return cur_item
    return max_item
 def most_common(lst):
    if max([lst.count(i)for i in lst]) == 1:
        return False
    else:
        return max(set(lst), key=lst.count)

以Luiz的回答为基础,但满足“在抽取索引最低的项目时应返回”的条件:

from statistics import mode, StatisticsError

def most_common(l):
    try:
        return mode(l)
    except StatisticsError as e:
        # will only return the first element if no unique mode found
        if 'no unique mode' in e.args[0]:
            return l[0]
        # this is for "StatisticsError: no mode for empty data"
        # after calling mode([])
        raise

例子:

>>> most_common(['a', 'b', 'b'])
'b'
>>> most_common([1, 2])
1
>>> most_common([])
StatisticsError: no mode for empty data