From: James Edward Gray II <james@...>
Date: 2007-02-26T02:20:00+09:00
Subject: Re: extract a random number of items from an array

On Feb 25, 2007, at 11:15 AM, Josselin 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 ?

Exactly.  Using rand(10) you would have a 1 in 10 chance that each  
number is added the the result set.

James Edward Gray II