油藏取样 [英] Reservoir sampling

问题描述

为了从不确定大小的数组中检索 k 个随机数，我们使用了一种称为水库采样的技术.任何人都可以用示例代码简要强调一下它是如何发生的吗?

To retrieve k random numbers from an array of undetermined size we use a technique called reservoir sampling. Can anybody briefly highlight how it happens with a sample code?

推荐答案

我其实没有意识到有一个名字，所以我从头开始证明并实现了:

I actually did not realize there was a name for this, so I proved and implemented this from scratch:

import random
def random_subset( iterator, K ):
    result = []
    N = 0

    for item in iterator:
        N += 1
        if len( result ) < K:
            result.append( item )
        else:
            s = int(random.random() * N)
            if s < K:
                result[ s ] = item

    return result

来自:http://web.archive.org/web/20141026071430/http://propersubset.com:80/2010/04/choosing-random-elements.html

接近尾声的证明.

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