如何检查列表中是否有超过 3 个相同的字符串，Python

Question

我有一个列表，如下所示：

a = ['www.hughes-family.org', 'www.bondedsender.com', 'thinkgeek.com', 'www.hughes-family.org', 'www.hughes-family.org', 'lists.sourceforge.net', 'www.hughes-family.org']

如何检查此列表中是否有超过三个相同的 url？我试过 set() 函数，但只要有重复的 url，它就会显示。这是我试过的：

if len(set(a)) < len(a):

Answer 1

使用Counter.most_common:

>>> Counter(a).most_common(1)[0][1]
4

这个returns最常见元素出现的次数。

Answer 2

您可以使用 list.count 获取出现三次或更多次的网址的数量：

urls = ['www.hughes-family.org', 'www.bondedsender.com', 'thinkgeek.com', 'www.hughes-family.org', 'www.hughes-family.org', 'lists.sourceforge.net', 'www.hughes-family.org']
new_urls = [url for url in urls if urls.count(url) > 1]
if len(new_urls) > 3:
    pass #condition met

Answer 3

你可以使用 dict 来捕捉重复的东西:

a = ['www.hughes-family.org', 'www.bondedsender.com', 'thinkgeek.com', 'www.hughes-family.org', 'www.hughes-family.org', 'lists.sourceforge.net', 'www.hughes-family.org']

count={}
for i,j in enumerate(a):
    if j not in count:
        count[j]=[i]
    else:
        count[j].append(i)


for i,j in count.items():
    if len(j)>1:
        #do you stuff

print(count)

输出：

{'www.hughes-family.org': [0, 3, 4, 6], 'thinkgeek.com': [2], 'www.bondedsender.com': [1], 'lists.sourceforge.net': [5]}

您可以使用 defaultdict 的第二种方法：

import collections

d=collections.defaultdict(list)
for i,j in enumerate(a):
    d[j].append(i)

print(d)

Answer 4

我假设您想检查是否有任何 URL 在列表中出现超过 3 次。您可以遍历列表，并创建一个包含字符串作为键的字典，并将它们各自的计数作为值（类似于 collections.Counter 的输出）。

In [1]: a = ['www.hughes-family.org', 'www.bondedsender.com', 'thinkgeek.com', '
   ...: www.hughes-family.org', 'www.hughes-family.org', 'lists.sourceforge.net'
   ...: , 'www.hughes-family.org']

In [2]: is_present = False

In [3]: url_counts = dict()

In [4]: for url in a:
    ...:     if not url_counts.get(url, None):  # If the URL is not present as a key, insert the URL with value 0
    ...:         url_counts[url] = 0
    ...:     url_counts[url] += 1  # Increment count
    ...:     if url_counts[url] > 3:  # Check if the URL occurs more than three times
    ...:         print "The URL ", url, " occurs more than three times!"
    ...:         is_present = True
    ...:         break  # Come out of the loop if any one of the URLs occur more than three times

# output - The URL  www.hughes-family.org  occurs more than three times!

In [5]: is_present  # To check if there is a URL which occurs more than three times
Out[5]: True

如何检查列表中是否有超过 3 个相同的字符串，Python

How to check if there are more than 3 identical string in a list, Python

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