我需要在随机位置填充几个 1 的列表。我可以成功地创建一个随机数列表：
from random import randint
l = [randint(0,1023) for _ in range(0,10)]
如何在 l 指定的位置填充 1 的列表？
问问题
525 次
4 回答
8
我需要在随机位置创建一个包含 10 - 40 l 的 0 的大列表来对算法进行基准测试。
这对你有用吗？
import random
zeros = [0] * 1024
ones = [1] * random.randint(10, 40)
l = zeros + ones
random.shuffle(l)
# the list l contains many zeros and 10 - 40 1's in random places.
where_the_ones_are = [i for i, x in enumerate(l) if x == 1]
于 2013-07-08T09:26:28.120 回答
7
稀疏列表
我对“稀疏列表”的理解是，大多数（例如，超过 95% 的）值将为零，并且出于内存效率的原因，您不希望存储这些值（参见 稀疏数组）。
列表理解
使用您的列表理解，您可以使用条件表达式解析( foo if 条件 else 栏) 来确定该位置是 1 还是 0。例如：
In [1]: from random import randint
In [2]: l = [randint(0,1023) for _ in range(0,10)]
In [3]: l
Out[3]: [987, 356, 995, 192, 21, 22, 1013, 375, 796, 339]
In [4]: 1 if 987 in l else 0
Out[4]: 1
In [5]: 1 if 988 in l else 0
Out[5]: 0
这意味着您不需要填充您在问题中提到的第二个列表，您只需遍历 0 - 1023 范围并使用：
1 if index in l else 0
字典理解
或者，您可以使用字典理解。我认为这更具可读性：
In [1]: from random import randint
In [2]: l = {randint(0, 1023): 1 for _ in xrange(0, 10)}
这将生成一个像这样的字典：
In [3]: l
Out[3]:
{216: 1,
381: 1,
384: 1,
392: 1,
396: 1,
472: 1,
585: 1,
630: 1,
784: 1,
816: 1}
然后访问元素，指定默认值为零。如果设置了请求位置的值，您将得到一个：
In [4]: l.get(216, 0)
Out[4]: 1
如果未设置该值，您将得到一个零：
In [5]: l.get(217, 0)
Out[5]: 0
获取职位列表：
In [6]: l.keys()
Out[6]: [384, 392, 472, 630, 216, 585, 396, 381, 784, 816]
上述两种方法的缺陷
randint(0, 1023)可能会多次发出相同的数字，从而导致冲突，这将导致少于所需的数量。
将它们捆绑在一起
我会将基于字典的实现包装在 aclass中，以使其易于（重新）使用。
from random import randint
class RandomSparseList(object):
def __init__(self, size, min_bits, max_bits):
self.size = int(size)
self.bits = {}
self.bits_set = randint(min_bits, max_bits)
while self.bits_set > len(self.bits):
self.bits[randint(0, self.size)] = 1
def __len__(self):
return self.size
def __getitem__(self, index):
if index < 0 or index >= self.size:
raise IndexError
return self.bits.get(int(index), 0)
def __iter__(self):
for i in xrange(self.size):
yield self.__getitem__(i)
def __contains__(self, index):
return index in self.bits
def __repr__(self):
return '[{}]'.format(', '.join(str(x) for x in self))
def set_bits(self):
return self.bits.keys()
示例用法
我已经把它class放在一个文件中：
In [1]: from random_sparse_list import RandomSparseList
创建一个实例：
In [2]: rsl = RandomSparseList(1024, 10, 40)
检查列表的长度：
In [3]: len(rsl)
Out[3]: 1024
设置了哪些位？
In [4]: rsl.set_bits()
Out[4]:
[523,
400,
285,
158,
419,
434,
701,
67,
843,
846,
591,
720,
470,
864,
912,
739,
996,
485,
489,
234,
1005,
573,
381,
784]
24：肯定在 10-40 的范围内
随机访问：
In [5]: rsl[523]
Out[5]: 1
In [6]: rsl[524]
Out[6]: 0
是不是有点设置？
In [7]: 400 in rsl
Out[7]: True
In [8]: 401 in rsl
Out[8]: False
迭代列表：
In [9]: for index, value in enumerate(rsl):
...: if value:
...: print '{} found at index {}'.format(value, index)
...:
1 found at index 67
1 found at index 158
1 found at index 234
1 found at index 285
1 found at index 381
1 found at index 400
1 found at index 419
1 found at index 434
1 found at index 470
1 found at index 485
1 found at index 489
1 found at index 523
1 found at index 573
1 found at index 591
1 found at index 701
1 found at index 720
1 found at index 739
1 found at index 784
1 found at index 843
1 found at index 846
1 found at index 864
1 found at index 912
1 found at index 996
1 found at index 1005
字符串表示：
In [10]: rsl
Out[10]: [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]
笔记
基于-set的实现将更加节省内存，但上面的dict0可以很容易地更改为包含除and之外的（随机或其他）值1。
更新
受这个问题和缺乏标准稀疏list实现的启发，我在 Cheese Shop 中添加了一个 sparse_list实现。您可以安装它，pip install sparse_list然后RandomSparseList实现对您来说更简单：
from sparse_list import SparseList
from random import randint
class RandomSparseList(SparseList):
def __init__(self, size, min_bits, max_bits):
super(RandomSparseList, self).__init__(size, 0)
self.bits = randint(min_bits, max_bits)
while self.bits > len(self.elements):
self.elements[randint(0, self.size)] = 1
这将与上面的示例完全相同，但有一些额外的功能，例如扩展切片。您可以阅读（并贡献）GitHub 上的源代码。
于 2013-07-08T09:40:07.340 回答
1
您可以使用此代码段：
ones_lst = [SOME_VALUE] * 1024
for val in l:
ones_lst[val] = 1
这里替换SOME_VALUE为您使用的不同值，除了一个（可能为零）
于 2013-07-08T09:10:23.263 回答
1
这是我的解决方案。位置和 1 的数量都是随机的。您将拥有一个数组中的位置来检查您的算法是否有效。
from random import randint
MAX_NUMS=1000
#big array of 0s
arr = [0] * MAX_NUMS
#How many 1s do you want?
numOnes=randint(10, 40)
ones=[1]*numOnes
#Fill array with random postions
for i in range(0,numOnes-1):
ones[i] = randint(0,MAX_NUMS-1)
print ones
#Set arr to 1 for each random postion
for pos in ones:
arr[pos]=1
print arr
于 2013-07-08T10:17:04.643 回答