From: Robert Klemme <shortcutter@...>
Date: 2008-05-16T17:48:24+09:00
Subject: Re: Randomizing an Array?

2008/5/15 Joao Silva <rubyforum@thisisnotmyrealemail.com>:
> Florian Frank wrote:
>> Daniel Waite wrote:
>>> Florian Frank wrote:
>>>> Don't do this, better use (1..10).sort_by { rand }. Your version is
>>>> equivalent to (1..10).sort { 1 } and *always* creates the same
>>>> permutation for this array.
>>>
>>> It's random for me. Both work.
>>
>> No, really, it isn't. It may "look random", but try sorting (1..10) many
>> times and ponder the coincidence.
>
> That's because sort{ foo } expects foo to be in -1,0,1.

I don't think so - the sign is important:

irb(main):001:0> (1..10).sort { -1 }
=> [1, 2, 3, 7, 4, 9, 5, 8, 6, 10]
irb(main):002:0> (1..10).sort { 1 }
=> [10, 6, 1, 7, 3, 8, 5, 9, 4, 2]
irb(main):003:0> (1..10).sort { 10 }
=> [10, 6, 1, 7, 3, 8, 5, 9, 4, 2]
irb(main):004:0> (1..10).sort { -10 }
=> [1, 2, 3, 7, 4, 9, 5, 8, 6, 10]

> rand() is always [0, 1).

Did you mean [0,1[?

> rand(2)-1 is (-1,1) however and thus will work just fine. :)

rand(2)-1 is (-1,0). I would rather do rand(3)-1 or rand(2) - 0.5  -
But all this is worse than sort_by { rand } IMHO.

Kind regards

robert

-- 
use.inject do |as, often| as.you_can - without end