Code Snippet: Array.shuffle

[Stefan Arentz]

Here is another small Ruby code snippet that extends the Array class. Use
this to randomize the order of all entries in an Array.

class Array
def shuffle
self.each_index { |i| r = rand(self.length - 1);
self[i],self[r] = self[r],self[i] }
end
end

Works like this:

a = Array[1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
a.shuffle
==> [7, 10, 9, 6, 4, 8, 5, 3, 1, 2]

S.

[Jason Creighton]

On 08 Jul 2003 03:01:30 +0200
Stefan Arentz <stefan.arentz@soze.com> wrote:

>
> Here is another small Ruby code snippet that extends the Array class. Use
> this to randomize the order of all entries in an Array.
>
> class Array
> def shuffle
> self.each_index { |i| r = rand(self.length - 1);
> self[i],self[r] = self[r],self[i] }
> end
> end
>
> Works like this:
>
> a = Array[1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
> a.shuffle
> ==> [7, 10, 9, 6, 4, 8, 5, 3, 1, 2]

>> ary = (0..10).to_a

=> [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

>> ary.sort { rand(3)-1 }

=> [4, 6, 5, 0, 2, 3, 9, 7, 8, 1, 10]

.....of course, this probably won't produce as random as result, but it's easier to implement.

Jason Creighton

[Joe Gwozdecki]

"Brian Candler" <B.Candler@pobox.com> wrote in message
news:20030708063637.GA74975@uk.tiscali.com...

> On Tue, Jul 08, 2003 at 10:21:42AM +0900, Stefan Arentz

wrote:

> >
> > Here is another small Ruby code snippet that extends the

Array class. Use

> > this to randomize the order of all entries in an Array.
> >
> > class Array
> > def shuffle
> > self.each_index { |i| r = rand(self.length - 1);
> > self[i],self[r] = self[r],self[i] }
> > end
> > end

>
> rand(x) gives a number between 0 and x-1, so I think you

should use

> rand(self.length) not rand(self.length-1). In particular

this will work

> properly for arrays containing 1 element.
>
> You could also replace self.each_index and self.length

with

> each_index and length, respectively. And you don't need

the semicolon.

>
> Regards,
>
> Brian.
>

How come when I try out this code snippet in IRB, including
entering the array, it does nothing? Am I missing
something?

Joe Gwozdecki
Houston, Texas

[Brian Candler]

On Wed, Jul 09, 2003 at 06:05:28AM +0900, Joe Gwozdecki wrote:

> How come when I try out this code snippet in IRB, including
> entering the array, it does nothing? Am I missing
> something?

I don't know. Here's an irb session log:

$ irb
irb(main):001:0> class Array
irb(main):002:1> def shuffle
irb(main):003:2> each_index { |i| r = rand(length)
irb(main):004:3> self[i],self[r] = self[r],self[i] }
irb(main):005:2> end
irb(main):006:1> end
=> nil
irb(main):007:0> a = [1,2,3,4,5,6,7,8,9,10]
=> [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
irb(main):008:0> a.shuffle
=> [8, 7, 1, 4, 9, 10, 3, 2, 6, 5]
irb(main):009:0> a.shuffle
=> [7, 10, 5, 9, 8, 1, 6, 3, 4, 2]
irb(main):010:0>

What did you do differently? Note that if you miss a bracket or an 'end'
then irb may think you are in a continuation line; if the prompt ends with
an asterisk this is a pretty strong clue.

irb(main):012:0> [
irb(main):013:1* 1,2,3
irb(main):014:1> ]
=> [1, 2, 3]

Regards,

Brian.

[Joe Gwozdecki]

"Brian Candler" <B.Candler@pobox.com> wrote in message
news:20030708224157.GA75351@uk.tiscali.com...

> On Wed, Jul 09, 2003 at 06:05:28AM +0900, Joe Gwozdecki

wrote:

> > How come when I try out this code snippet in IRB,

including

> > entering the array, it does nothing? Am I missing
> > something?

>
> I don't know. Here's an irb session log:
>
> $ irb
> irb(main):001:0> class Array
> irb(main):002:1> def shuffle
> irb(main):003:2> each_index { |i| r = rand(length)
> irb(main):004:3> self[i],self[r] = self[r],self[i] }
> irb(main):005:2> end
> irb(main):006:1> end
> => nil
> irb(main):007:0> a = [1,2,3,4,5,6,7,8,9,10]
> => [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
> irb(main):008:0> a.shuffle
> => [8, 7, 1, 4, 9, 10, 3, 2, 6, 5]
> irb(main):009:0> a.shuffle
> => [7, 10, 5, 9, 8, 1, 6, 3, 4, 2]
> irb(main):010:0>
>
> What did you do differently? Note that if you miss a

bracket or an 'end'

> then irb may think you are in a continuation line; if the

prompt ends with

> an asterisk this is a pretty strong clue.
>
> irb(main):012:0> [
> irb(main):013:1* 1,2,3
> irb(main):014:1> ]
> => [1, 2, 3]
>
> Regards,
>
> Brian.
>

Your coding works fine in IRB. The original poster wrote a
= Array[1,2,3,4,5,6,7,8,9,10] which did not work. Get rid
of "Array" and it works.

Joe Gwozdecki
Houston, Texas

[Brian Candler]

On Wed, Jul 09, 2003 at 08:46:38AM +0900, Joe Gwozdecki wrote:

> Your coding works fine in IRB. The original poster wrote a
> = Array[1,2,3,4,5,6,7,8,9,10] which did not work. Get rid
> of "Array" and it works.

It looks OK to me:

irb(main):001:0> a = Array[1,2,3,4,5]
=> [1, 2, 3, 4, 5]
irb(main):002:0>

(this is 1.6.8)

[Joe Gwozdecki]

"Brian Candler" <B.Candler@pobox.com> wrote in message
news:20030709073944.GA75875@uk.tiscali.com...

> On Wed, Jul 09, 2003 at 08:46:38AM +0900, Joe Gwozdecki

wrote:

> > Your coding works fine in IRB. The original poster

wrote a

> > = Array[1,2,3,4,5,6,7,8,9,10] which did not work. Get

rid

> > of "Array" and it works.

>
> It looks OK to me:
>
> irb(main):001:0> a = Array[1,2,3,4,5]
> => [1, 2, 3, 4, 5]
> irb(main):002:0>
>
> (this is 1.6.8)
>

I got the error from -- a = array[1,2,3,4,5]
IRB will give a consistent error.
You are right. a = Array[1,2,3,4,5] does
work just fine. Also a = [1,2,3,4,5] does too
and is probably cleaner.

Joe Gwozdecki
Houston, Texas

[Brian Candler]

On Wed, Jul 09, 2003 at 08:50:59PM +0900, Joe Gwozdecki wrote:

> > It looks OK to me:
> >
> > irb(main):001:0> a = Array[1,2,3,4,5]
> > => [1, 2, 3, 4, 5]
> > irb(main):002:0>
> >
> > (this is 1.6.8)
> >

>
> I got the error from -- a = array[1,2,3,4,5]
> IRB will give a consistent error.

Certainly. Ruby is case-sensitive. You need to call method [] of 'Array',
not 'array'

Cheers,

Brian.

[Mauricio Fernández]

On Wed, Jul 09, 2003 at 09:35:22PM +0900, Brian Candler wrote:

> On Wed, Jul 09, 2003 at 08:50:59PM +0900, Joe Gwozdecki wrote:

> > > It looks OK to me:
> > >
> > > irb(main):001:0> a = Array[1,2,3,4,5]
> > > => [1, 2, 3, 4, 5]
> > > irb(main):002:0>
> > >
> > > (this is 1.6.8)
> > >

> >
> > I got the error from -- a = array[1,2,3,4,5]
> > IRB will give a consistent error.

>
> Certainly. Ruby is case-sensitive. You need to call method [] of 'Array',
> not 'array'

It's not Array.[], but Kernel#Array.

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Running Debian GNU/Linux Sid (unstable)
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Software is like sex; it's better when it's free.
-- Linus Torvalds

[Brian Candler]

On Wed, Jul 09, 2003 at 09:45:33PM +0900, Mauricio Fernández wrote:

> > > I got the error from -- a = array[1,2,3,4,5]
> > > IRB will give a consistent error.

> >
> > Certainly. Ruby is case-sensitive. You need to call method [] of 'Array',
> > not 'array'

>
> It's not Array.[], but Kernel#Array.

You sure? This is Kernel#Array:

Array(5) #>> [5]

Array(5,6) #>> ArgumentError: wrong # of arguments(2 for 1)

I believe that foo[bar] is a shortcut for

foo.send(:[], bar)

And therefore Array[1,2,3,4,5] is

Array.send(:[], 1, 2, 3, 4, 5)
#=> [1, 2, 3, 4, 5]

or equivalently

Array.[] (1,2,3,4,5)
#=> [1, 2, 3, 4, 5]

i.e. this is a class (singleton) method of Array

Regards,

Brian.

[Brian Candler]

On Thu, Jul 10, 2003 at 12:16:59AM +0900, Mauricio Fernández wrote:

> Anyway, this is yet another case of significant spaces in Ruby:
>

> >> class << Array
> >> alias_method :_old_, :[];

> ?> def [](*a)

> >> puts "Array.[]"
> >> _old_(*a)
> >> end
> >> end

> => nil

> >> Array[1,2,3]

> Array.[]
> => [1, 2, 3]

> >> Array [1,2,3]

> => [1, 2, 3]

Ah, I see: foo[bar] => foo.[] (bar)
foo [bar] => foo( [bar] )

Yuk. This exists in 1.6.8. I guess it mirrors Matz's change introduced for
1.8:
foo(a+b).c => ( foo(a+b) ).c
foo (a+b).c => foo( (a+b).c )

As for the semicolon, it seems that irb does not play nicely with unusual
symbols:

$ irb
irb(main):001:0> :ok
=> :ok
irb(main):002:0> :[]
irb(main):003:0* puts "oops"
oops
=> nil
irb(main):004:0>

Cheers,

Brian.