如何在整数列表中找到重复项并创建重复项的另一个列表?
当前回答
集合。Counter是python 2.7中的新功能:
Python 2.5.4 (r254:67916, May 31 2010, 15:03:39)
[GCC 4.1.2 20080704 (Red Hat 4.1.2-46)] on linux2
a = [1,2,3,2,1,5,6,5,5,5]
import collections
print [x for x, y in collections.Counter(a).items() if y > 1]
Type "help", "copyright", "credits" or "license" for more information.
File "", line 1, in
AttributeError: 'module' object has no attribute 'Counter'
>>>
在早期版本中,你可以使用传统的字典:
a = [1,2,3,2,1,5,6,5,5,5]
d = {}
for elem in a:
if elem in d:
d[elem] += 1
else:
d[elem] = 1
print [x for x, y in d.items() if y > 1]
其他回答
通过检查出现的次数,简单地遍历列表中的每个元素,然后将它们添加到一个集,然后打印重复的元素。希望这能帮助到一些人。
myList = [2 ,4 , 6, 8, 4, 6, 12];
newList = set()
for i in myList:
if myList.count(i) >= 2:
newList.add(i)
print(list(newList))
## [4 , 6]
还有其他测试。当然要做……
set([x for x in l if l.count(x) > 1])
...代价太大了。使用下一个final方法大约快500倍(数组越长结果越好):
def dups_count_dict(l):
d = {}
for item in l:
if item not in d:
d[item] = 0
d[item] += 1
result_d = {key: val for key, val in d.iteritems() if val > 1}
return result_d.keys()
只有2个循环,没有非常昂贵的l.count()操作。
下面是一个比较方法的代码。代码如下,输出如下:
dups_count: 13.368s # this is a function which uses l.count()
dups_count_dict: 0.014s # this is a final best function (of the 3 functions)
dups_count_counter: 0.024s # collections.Counter
测试代码:
import numpy as np
from time import time
from collections import Counter
class TimerCounter(object):
def __init__(self):
self._time_sum = 0
def start(self):
self.time = time()
def stop(self):
self._time_sum += time() - self.time
def get_time_sum(self):
return self._time_sum
def dups_count(l):
return set([x for x in l if l.count(x) > 1])
def dups_count_dict(l):
d = {}
for item in l:
if item not in d:
d[item] = 0
d[item] += 1
result_d = {key: val for key, val in d.iteritems() if val > 1}
return result_d.keys()
def dups_counter(l):
counter = Counter(l)
result_d = {key: val for key, val in counter.iteritems() if val > 1}
return result_d.keys()
def gen_array():
np.random.seed(17)
return list(np.random.randint(0, 5000, 10000))
def assert_equal_results(*results):
primary_result = results[0]
other_results = results[1:]
for other_result in other_results:
assert set(primary_result) == set(other_result) and len(primary_result) == len(other_result)
if __name__ == '__main__':
dups_count_time = TimerCounter()
dups_count_dict_time = TimerCounter()
dups_count_counter = TimerCounter()
l = gen_array()
for i in range(3):
dups_count_time.start()
result1 = dups_count(l)
dups_count_time.stop()
dups_count_dict_time.start()
result2 = dups_count_dict(l)
dups_count_dict_time.stop()
dups_count_counter.start()
result3 = dups_counter(l)
dups_count_counter.stop()
assert_equal_results(result1, result2, result3)
print 'dups_count: %.3f' % dups_count_time.get_time_sum()
print 'dups_count_dict: %.3f' % dups_count_dict_time.get_time_sum()
print 'dups_count_counter: %.3f' % dups_count_counter.get_time_sum()
要删除重复项,请使用集合(a)。要打印副本,可以这样做:
a = [1,2,3,2,1,5,6,5,5,5]
import collections
print([item for item, count in collections.Counter(a).items() if count > 1])
## [1, 2, 5]
请注意Counter并不是特别有效(计时),可能会在这里过度使用。Set会表现得更好。这段代码以源顺序计算一个唯一元素的列表:
seen = set()
uniq = []
for x in a:
if x not in seen:
uniq.append(x)
seen.add(x)
或者,更简洁地说:
seen = set()
uniq = [x for x in a if x not in seen and not seen.add(x)]
我不推荐后一种风格,因为它不清楚not seen.add(x)在做什么(set add()方法总是返回None,因此需要not)。
计算没有库的重复元素列表:
seen = set()
dupes = []
for x in a:
if x in seen:
dupes.append(x)
else:
seen.add(x)
或者,更简洁地说:
seen = set()
dupes = [x for x in a if x in seen or seen.add(x)]
如果列表元素不可哈希,则不能使用set /dicts,必须使用二次时间解决方案(逐个比较)。例如:
a = [[1], [2], [3], [1], [5], [3]]
no_dupes = [x for n, x in enumerate(a) if x not in a[:n]]
print no_dupes # [[1], [2], [3], [5]]
dupes = [x for n, x in enumerate(a) if x in a[:n]]
print dupes # [[1], [3]]
如果你不关心自己编写算法或使用库,Python 3.8一行代码:
l = [1,2,3,2,1,5,6,5,5,5]
res = [(x, count) for x, g in groupby(sorted(l)) if (count := len(list(g))) > 1]
print(res)
打印项目和计数:
[(1, 2), (2, 2), (5, 4)]
groupby接受一个分组函数,因此您可以以不同的方式定义分组,并根据需要返回额外的Tuple字段。
第三个接受答案的例子给出了一个错误的答案,并且没有试图给出重复的答案。下面是正确的版本:
number_lst = [1, 1, 2, 3, 5, ...]
seen_set = set()
duplicate_set = set(x for x in number_lst if x in seen_set or seen_set.add(x))
unique_set = seen_set - duplicate_set
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