From: Josselin <josselin@...>
Date: 2007-02-26T02:15:06+09:00
Subject: Re: extract a random number of items from an array

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 ?