From: Matt Chen <chen.mingquan@...>
Date: 2007-02-26T01:59:50+09:00
Subject: Re: extract a random number of items from an array

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Here is my solution, it should be work.


----
def extract_values(array, n)
    len = array.length
    (len - 1).downto(len - n) do |i|
        sway_index = rand(len) % i
        array[i], array[sway_index] = array[sway_index], array[i]
    end

    return array[len-n..len-1]
end



On 2/26/07, James Edward Gray II <james@grayproductions.net> wrote:
>
> On Feb 25, 2007, at 10:20 AM, Josselin wrote:
>
> > given an array of values, how should I extract an random number of
> > these values
> >
> > a = [13, 15, 17, 18, 19, 20, 21, 23, 24, 25, 26, 27, 28, 29, 30,
> > 31, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56,
> > 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73,
> > 74, 75, 76, 77, 78, 79, 81, 82, 83, 84, 85, 86, 88, 89, 90, 91, 92,
> > 93, 94, 95, 96, 97, 98, 99, 100, 101, 102, 103, 104, 105, 106]
>
> Just give a random chance that a value is added to the result set:
>
> >> a.select { rand(2).zero? }
> => [13, 15, 23, 24, 25, 26, 27, 28, 29, 31, 41, 42, 44, 45, 46, 47,
> 49, 51, 52, 53, 55, 58, 60, 61, 62, 66, 67, 68, 69, 70, 71, 72, 73,
> 75, 76, 78, 81, 82, 83, 89, 90, 91, 94, 95, 98, 99, 100, 101, 103,
> 104, 105, 106]
> >> a.select { rand(2).zero? }
> => [13, 18, 19, 20, 21, 24, 26, 27, 28, 29, 30, 31, 41, 42, 44, 48,
> 49, 51, 52, 53, 55, 57, 58, 59, 62, 63, 64, 66, 68, 70, 79, 81, 82,
> 83, 86, 89, 90, 91, 92, 94, 97, 98, 102, 104, 105, 106]
> >> a.select { rand(2).zero? }
> => [15, 17, 18, 19, 20, 21, 23, 25, 30, 41, 44, 45, 46, 49, 50, 51,
> 52, 53, 54, 57, 59, 63, 64, 66, 68, 70, 72, 73, 76, 78, 79, 81, 82,
> 90, 91, 95, 97, 101, 102, 104]
>
> Hope that helps.
>
> James Edward Gray II
>
>

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