From: Mingquan Chen <chen.mingquan@...>
Date: 2007-02-26T02:29:02+09:00
Subject: Re: extract a random number of items from an array

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If you use this way, then how we you get exactly n values randomly from the
given array?

I doubt the correct of this way.

My solution should meet your requirement. :-)

On 2/26/07, Josselin <josselin@wanadoo.fr> wrote:
>
> On 2007-02-25 17:41:58 +0100, James Edward Gray II
> <james@grayproductions.net> said:
>
> > 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
>
> thanks James that's exactly what I need
> I made various tests like     a.select { rand(10).zero? }
> and I got different results..  as I want
>
> I try to understand the logic behind your solution (not to dry stupid...)
>
> select from array a  ...  {  for each item.  0#no 1#yes }   ok for
> rand(2)  , if I use rand(10) less chances to get it
> is that right ?
>
>
>

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