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comp.lang.ruby

Randomizing an Array?

jwcooper

12/22/2006 7:35:00 PM

I'm trying to randomize an array, and this is what I have:

arr_set_unordered = randomizer(arr_set)

def randomizer(arr)
result = arr.collect { arr.slice!(rand arr.length) }
end

It does randomize it, but it only returns 3 values instead of the 5
values that I'm expecting. Any ideas why?

Thank you!
11 Answers

Daniel Waite

12/29/2006 8:15:00 PM

0

jwcooper wrote:
> I'm trying to randomize an array...

Try this.

class Array

def randomize
duplicated_original, new_array = self.dup, self.class.new
new_array <<
duplicated_original.slice!(rand(duplicated_original.size)) until
new_array.size.eql?(self.size)
new_array
end

def randomize!
self.replace(randomize)
end

end

Enjoy!

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Daniel Waite

12/29/2006 8:18:00 PM

0

Sorry, I guess a use-case would be helpful.

Call #randomize or #randomize! on any array to mix up its elements.

[ 5, 10, 15, 20, 25 ].randomize # [25, 15, 5, 20, 10]


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Dan Stevens (IAmAI)

12/30/2006 3:32:00 PM

0

I found a library called 'rand.rb':
http://raa.ruby-lang.org/pro.... It allows you to select an
element at random from an array and 'scramble' (randomize the order)
of them as well.

Description:

Helper methods for Enumerable, Array, Hash, and String
that let you pick a random item or shuffle the order of items.

Examples with Array:

[1,2,3,4].pick
# => 2 (pick random element)

[1,2,3,4].shuffle
# => [2, 4, 1, 3] (return random-sorted version)

a = [1,2,3,4]
a.pick!
# => 3
a
# => [1,2,4] (remove the picked element)

On 29/12/06, Daniel Waite <rabbitblue@gmail.com> wrote:
> Sorry, I guess a use-case would be helpful.
>
> Call #randomize or #randomize! on any array to mix up its elements.
>
> [ 5, 10, 15, 20, 25 ].randomize # [25, 15, 5, 20, 10]
>
>
> --
> Posted via http://www.ruby-....
>
>

Ilan Berci

1/2/2007 4:37:00 PM

0

jwcooper wrote:
> I'm trying to randomize an array, and this is what I have:
>
> arr_set_unordered = randomizer(arr_set)
>
> def randomizer(arr)
> result = arr.collect { arr.slice!(rand arr.length) }
> end
>
> It does randomize it, but it only returns 3 values instead of the 5
> values that I'm expecting. Any ideas why?
>
> Thank you!

ilans-Mac:~ ilan$ irb
irb(main):001:0> (1..10).to_a.sort {rand}
=> [10, 6, 1, 7, 3, 8, 5, 9, 4, 2]
irb(main):002:0>

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Florian Frank

1/2/2007 9:03:00 PM

0

Ilan Berci wrote:
> jwcooper wrote:
>
>> I'm trying to randomize an array, and this is what I have:
>>
[...]
> ilans-Mac:~ ilan$ irb
> irb(main):001:0> (1..10).to_a.sort {rand}
> => [10, 6, 1, 7, 3, 8, 5, 9, 4, 2]
> irb(main):002:0>
>
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.

--
Florian Frank

Daniel Waite

1/9/2007 7:30:00 PM

0

Florian Frank wrote:
>> irb(main):001:0> (1..10).to_a.sort {rand}
>> => [10, 6, 1, 7, 3, 8, 5, 9, 4, 2]

Wow. That is squeaky clean, and a lot faster than my method. Thanks for
sharing. :)

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Daniel Waite

1/9/2007 7:35:00 PM

0

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.

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Ilan Berci

1/9/2007 9:00:00 PM

0

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.

Actually Frank is correct, my mistake, it should definetely be sort_by
and not sort.. I should have reviewed it more thoroughly before
responding..

ilan



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Florian Frank

1/9/2007 10:10:00 PM

0

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.

--
Florian Frank

Joao Silva

5/15/2008 8:53:00 PM

0

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.

rand() is always [0, 1).

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

One could do sort{rand <=> rand}, but that's ~9x slower by my testing.

irb(main):163:0> (1..10).to_a.sort{rand }
=> [10, 6, 1, 7, 3, 8, 5, 9, 4, 2]
irb(main):164:0> (1..10).to_a.sort{rand }
=> [10, 6, 1, 7, 3, 8, 5, 9, 4, 2]
irb(main):165:0> (1..11).to_a.sort{rand }
=> [11, 6, 1, 7, 3, 8, 5, 9, 4, 10, 2]
irb(main):166:0> (1..12).to_a.sort{rand }
=> [12, 7, 1, 8, 3, 9, 5, 10, 2, 11, 6, 4]

vs

irb(main):186:0> (1..12).to_a.sort{rand(2) -1}
=> [1, 2, 6, 11, 9, 4, 8, 7, 5, 10, 3, 12]
irb(main):187:0> (1..12).to_a.sort{rand(2) -1}
=> [1, 9, 8, 3, 5, 6, 11, 4, 2, 10, 7, 12]


- Sai http://..., who is too lazy to remember his actual account
pass right now
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