使用随机1填充稀疏列表

时间：2013-07-08 09:06:26

标签： python

我需要在随机位置填充一些带有1个的列表。我可以成功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

4 个答案:

答案 0 :(得分：8)

  

我需要在随机位置创建一个0到40的大型列表   对算法进行基准测试。

这可能适合你吗？

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]

答案 1 :(得分：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< / em>这些（ cf。 Sparse array）。

列表理解

使用您的列表理解，您可以使用Conditional Expression Resolution（ foo if 条件 else 栏）确定一个或零是否在该位置。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，您可以迭代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dictionary comprehension。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)}

这将生成如下字典：

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，您将获得零：

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]

上述两种方法中的缺陷

randint(0, 1023)可以多次发出相同的数字，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class中，以便于（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()

使用示例

我把这个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：这肯定在10-40之间。

随机存取：

In [5]: rsl[523]
Out[5]: 1

In [6]: rsl[524]
Out[6]: 0

有点设置？

In [7]: 400 in rsl
Out[7]: True

In [8]: 401 in rsl
Out[8]: False

对列表进行迭代：

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]

注意

基于set的实施可以提高内存效率，但上面的dict可以轻松更改为包含0和{{1}以外的（随机或其他）值}。

更新

受此问题的启发以及缺乏标准的稀疏1实施，我在奶酪店添加了sparse_list实施。您可以使用list进行安装，然后pip install sparse_list实施对您来说更简单：

RandomSparseList

这将与上面的示例完全相同，但有一些额外内容，如扩展切片。您可以阅读（并参与）源on GitHub。

答案 2 :(得分：1)

您可以使用此代码段：

ones_lst = [SOME_VALUE] * 1024
for val in l:
  ones_lst[val] = 1

此处将SOME_VALUE替换为您使用的不同值，除了一个（可能为零）

答案 3 :(得分：1)

这是我的解决方案。位置和1的数量都是随机的。你将在一个数组中有位置来检查你的算法是否有效。

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
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