From: "Jesús Gabriel y Galán" <jgabrielygalan@...>
Date: 2013-01-31T19:25:28+09:00
Subject: Re: Select "columns" from multidimensional array?

On Thu, Jan 31, 2013 at 10:46 AM, Joel Pearson <lists@ruby-forum.com> wrote:
> There's probably a simpler answer to this than the ways I've come up
> with.
> What's the best way to select columns from a two-dimensional array?
>
> I build arrays to match excel-style formatting, like this but larger:
> __________________
>
> a = [
>   [ 'A1', 'A2', 'A3' ],
>   [ 'B1', 'B2', 'B3' ],
>   [ 'C1', 'C2', 'C3' ]
> ]
>
> def get_cols (multi_array, headers )
>
>   indices = []
>   headers.each { |val| indices << multi_array[0].index(val) }
>   indices.compact!
>
>   multi_array.map do |ar|
>     indices.map { |idx| ar[idx] }
>   end
>
> end
>
> get_cols a, %w(A1 A3)
>
> => [["A1", "A3"], ["B1", "B3"], ["C1", "C3"]]

Is this the desired output?

For getting the columns filtering the ones that have a header:

def get_cols(multi_array, headers)
  multi_array.transpose.select {|(header,_)| headers.include? header}
end

1.9.2p290 :001 > a = [
1.9.2p290 :002 >       [ 'A1', 'A2', 'A3' ],
1.9.2p290 :003 >       [ 'B1', 'B2', 'B3' ],
1.9.2p290 :004 >       [ 'C1', 'C2', 'C3' ]
1.9.2p290 :005?>   ]
1.9.2p290 :008 > def get_cols(multi_array, headers)
1.9.2p290 :009?>     multi_array.transpose.select {|(header,_)|
headers.include? header}
1.9.2p290 :010?>   end
 => nil
1.9.2p290 :011 > get_cols a, %w(A1 A3)
 => [["A1", "B1", "C1"], ["A3", "B3", "C3"]]


Jesus.