From: Robert Dober <robert.dober@...>
Date: 2008-07-04T03:37:43+09:00
Subject: Re: pseudo-randomize an array in a consistent order

On Thu, Jul 3, 2008 at 6:08 PM, James Gray <james@grayproductions.net> wrote:
> On Jul 3, 2008, at 11:04 AM, Robert Dober wrote:
>
>> a.sort{ rand }
>
> Don't do that:
>
>>> a = (1..5).to_a
> => [1, 2, 3, 4, 5]
>>> a.sort { rand }
> => [5, 3, 1, 4, 2]
>>> a.sort { rand }
> => [5, 3, 1, 4, 2]
>>> a.sort { rand }
> => [5, 3, 1, 4, 2]
>
> Use a.sort_by { rand } instead.
>
> James Edward Gray II
>
>


James you should know me better ;) He does not want sort_by{ rand } he
explicitely asked for deterministic results, thus
   sort{ rand }.
But yet James is right of course, even if for the wrong reason here.
First of all you cannot set the seed, second of all it will not be
portable (jruby reverses for example, while ruby1.8 and ruby1.9 do the
same right now), and I guess that this is not guaranteed behavior at
all.

So after all I have to admit it was not my brightest idea to introduce
this "pattern" ;) OTOH I had worse ideas.

Cheers
Robert

-- 
http://ruby-smalltalk.blogspot.com/

---
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