From: Robert Klemme <shortcutter@...>
Date: 2013-02-12T21:29:20+09:00
Subject: Re: Select "columns" from multidimensional array?

On Tue, Feb 12, 2013 at 1:19 PM, Joel Pearson <lists@ruby-forum.com> wrote:
> I've decided to inherit from array after all, since all I want to do
> with this is extend support for multidimensional arrays, but without
> overwriting any of Array's methods.

I usually do not engage in predictions since I don't have a crystal
ball but in this case I'll say: you won't get happy with that
approach.  For example, anybody can override header values or complete
rows / columns violating your class's idea of internal state.

> Anyway, the obstacle I've hit is one I can avoid, but I was wondering
> whether I'm doing something wrong, or whether there's a nice Rubyish way
> around this. Here's a simplified version to demonstrate the issue:
>
> ___________________
> class Excel_Sheet<Array
>
>   def initialize( val=[] )
>     val = %w(A1 B1 C1 A2 B2 C2 A3 B3 C3).each_slice(3).to_a if val ==
> 'test'
>     super ( val )
>   end
>
>   def skip_headers
>     block_given? ? ( [ self[0] ] + yield( self[1..-1] ) ) : (
> self[1..-1] )
>   end

What is this supposed to do?  Ah, I think I see.  I'd probably name it
differently, i.e. each_data_cell or something.

>   def filter( header, regex )
>     idx = self[0].index header
>     skip_headers { |xl| xl.select { |ar| ar[idx] =~ regex } }
>   end
>
> end

That combines too much logic in one method IMHO.  I'd rather select a
row based on header and then I would use #select on that.

> So in short, my question is how can I return my class type after using
> Array's methods on my child-class?

Do you mean as return value from #map and the like?  Well, you can't
without overriding all methods with this approach, I'm afraid.  That's
one of the reasons why this approach does not work well. :-)

Kind regards

robert

-- 
remember.guy do |as, often| as.you_can - without end
http://blog.rubybestpractices.com/