# Strange Array behavior after upgrading to Rails 2.0.2

**URL:** <https://www.ruby-forum.com/t/strange-array-behavior-after-upgrading-to-rails-2-0-2/124424>\
**Category:** Rails\
**Created:** [December 28, 2007, 4:48pm UTC](https://www.ruby-forum.com/t/strange-array-behavior-after-upgrading-to-rails-2-0-2/124424 "2007-12-28T16:48:20Z")\
**Posts on this page:** 7\
**Page:** 1

<div class="post-metadata">

**Author:** ![tuktuk](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/77aa72/32.png) [@tuktuk](https://www.ruby-forum.com/u/tuktuk)\
**Post date:** [December 28, 2007, 4:48pm UTC](https://www.ruby-forum.com/t/strange-array-behavior-after-upgrading-to-rails-2-0-2/124424/1 "2007-12-28T16:48:20Z")

</div>

I’ve come around a strange problem, after upgrading to 2.0.2.

I have subclassed the Array class with this method to extract a random  
item (I haven’t made it myself, but it is quite clever):

class Array  
def random(weights=nil)  
return random(map {|n| n.send(weights)}) if weights.is\_a? Symbol

puts length  
puts self

```
weights ||= Array.new(length, 1.0)
total = weights.inject(0.0) {|t,w| t+w}
point = rand * total

zip(weights).each do |n,w|
  return n if w >= point
  point -= w
end

```

end  
end

If I use it with a simple array like:

arr = [5,8,7,3]  
arr.random

It works fine.

But if i try the same with a database extraction I now get an error. As  
an example, I have a model called “Banner”:

banner\_list = Banner.find(:all)  
banner\_list.random

This gives the following error:

* * *

## undefined method `\*’ for #Banner:0x489c3f4

The error occurs in the subclassing code at the following line:

point = rand \* total

The strange thing is, that this has worked with Rails 1.2.5, but when  
upgrading to 2.0.2, the error now occurs.

Does Rails 2.0.2 return results in another way than 1.2.5?

---

<div class="post-metadata">

**Author:** ![tuktuk](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/77aa72/32.png) [@tuktuk](https://www.ruby-forum.com/u/tuktuk)\
**Post date:** [December 28, 2007, 5:17pm UTC](https://www.ruby-forum.com/t/strange-array-behavior-after-upgrading-to-rails-2-0-2/124424/2 "2007-12-28T17:17:12Z")

</div>

Sorry I’ve made a slight typo (I was trying to find out what was  
happening…) The subclassing should look like this:

class Array  
def random(weights=nil)  
return random(map {|n| n.send(weights)}) if weights.is\_a? Symbol

```
weights ||= Array.new(length, 1.0)
total = weights.inject(0.0) {|t,w| t+w}
point = rand * total

zip(weights).each do |n,w|
  return n if w >= point
  point -= w
end

```

end  
end

---

<div class="post-metadata">

**Author:** ![tuktuk](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/77aa72/32.png) [@tuktuk](https://www.ruby-forum.com/u/tuktuk)\
**Post date:** [December 28, 2007, 9:56pm UTC](https://www.ruby-forum.com/t/strange-array-behavior-after-upgrading-to-rails-2-0-2/124424/3 "2007-12-28T21:56:46Z")

</div>

Rick Denatale wrote:

> I think that changing the line
> 
> point = rand \* total
> 
> to
> 
> point = Kernel::rand \* total
> 
> will fix this.

And indeed it did. Thank you very much! 🙂

- Carsten

---

<div class="post-metadata">

**Author:** ![tuktuk](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/77aa72/32.png) [@tuktuk](https://www.ruby-forum.com/u/tuktuk)\
**Post date:** [December 28, 2007, 6:39pm UTC](https://www.ruby-forum.com/t/strange-array-behavior-after-upgrading-to-rails-2-0-2/124424/4 "2007-12-28T18:39:10Z")

</div>

On Dec 28, 2007 10:48 AM, Carsten G.  
[removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> puts length  
> end  
> But if i try the same with a database extraction I now get an error. As  
> an example, I have a model called “Banner”:
> 
> banner\_list = Banner.find(:all)  
> banner\_list.random
> 
> This gives the following error:
> 
> * * *
> 
> undefined method `\*’ for #Banner:0x489c3f4

ActiveSupport now adds an Array#rand method which returns a random  
element, this overrides Kernel#rand which returns a float.

I think that changing the line

point = rand \* total

to

point = Kernel::rand \* total

will fix this.

–  
Rick DeNatale

My blog on Ruby  
[http://talklikeaduck.denhaven2.com/](http://talklikeaduck.denhaven2.com/)

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<div class="post-metadata">

**Author:** ![tuktuk](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/77aa72/32.png) [@tuktuk](https://www.ruby-forum.com/u/tuktuk)\
**Post date:** [December 28, 2007, 11:14pm UTC](https://www.ruby-forum.com/t/strange-array-behavior-after-upgrading-to-rails-2-0-2/124424/5 "2007-12-28T23:14:19Z")

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On Dec 28, 2007 4:27 PM, Mark W. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> > And indeed it did. Thank you very much! 🙂
> 
> Couldn’t you just use Array#rand ?

I thought of suggesting that, but he’s trying to do something similar,  
but with a parameter to provide a weighted distribution. The rand  
method in ActiveSupport only gives a uniform distribution.

It might be useful if this is only used with ActiveSupport to put  
something like

return rand unless weightt

at the top of the method though.

–  
Rick DeNatale

My blog on Ruby  
[http://talklikeaduck.denhaven2.com/](http://talklikeaduck.denhaven2.com/)

---

<div class="post-metadata">

**Author:** ![tuktuk](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/77aa72/32.png) [@tuktuk](https://www.ruby-forum.com/u/tuktuk)\
**Post date:** [December 28, 2007, 10:28pm UTC](https://www.ruby-forum.com/t/strange-array-behavior-after-upgrading-to-rails-2-0-2/124424/6 "2007-12-28T22:28:32Z")

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On Dec 28, 12:56 pm, Carsten G. \<rails-mailing-l…@andreas-  
[s.net](http://s.net)\> wrote:

> Rick Denatale wrote:
> 
> > I think that changing the line  
> > point = rand \* total  
> > to  
> > point = Kernel::rand \* total  
> > will fix this.
> 
> And indeed it did. Thank you very much! 🙂

Couldn’t you just use Array#rand ?

///ark

---

<div class="post-metadata">

**Author:** ![tuktuk](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/77aa72/32.png) [@tuktuk](https://www.ruby-forum.com/u/tuktuk)\
**Post date:** [December 29, 2007, 12:03am UTC](https://www.ruby-forum.com/t/strange-array-behavior-after-upgrading-to-rails-2-0-2/124424/7 "2007-12-29T00:03:50Z")

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Rick Denatale wrote:

> I thought of suggesting that, but he’s trying to do something similar,  
> but with a parameter to provide a weighted distribution. The rand  
> method in ActiveSupport only gives a uniform distribution.
> 
> It might be useful if this is only used with ActiveSupport to put  
> something like
> 
> return rand unless weightt
> 
> at the top of the method though.

You’re quite right Rick. The code could do with this refactoring, after  
all it IS pre-2.0 🙂 - thank you for your bright ideas.

I don’t recall who made this little nice function, but I think I’ll  
repost it on the net with modifications.

- Carsten