From: yermej <yermej@...>
Date: 2008-05-11T02:05:06+09:00
Subject: Re: Delete every other value in an array

On May 9, 10:08 am, "ara.t.howard" <ara.t.how...@gmail.com> wrote:
> On May 9, 2008, at 8:35 AM, yermej wrote:
>
> > a = %w(a b c d e f g h i j k)
> > 1.upto(a.size) {|i| a.delete_at i}
>
> it does, but accidentally:
>
> cfp:~ > cat a.rb
>
> a = %w(a b c d e f g h i j k)
>
> 1.upto(a.size) do |i|
>    puts '---'
>    p :i => i
>    p :before => a
>    a.delete_at i
>    p :after => a
> end
>
> cfp:~ > ruby a.rb
> ---
> {:i=>1}
> {:before=>["a", "b", "c", "d", "e", "f", "g", "h", "i", "j", "k"]}
> {:after=>["a", "c", "d", "e", "f", "g", "h", "i", "j", "k"]}
> ---
> {:i=>2}
> {:before=>["a", "c", "d", "e", "f", "g", "h", "i", "j", "k"]}
> {:after=>["a", "c", "e", "f", "g", "h", "i", "j", "k"]}
> ---
> {:i=>3}
> {:before=>["a", "c", "e", "f", "g", "h", "i", "j", "k"]}
> {:after=>["a", "c", "e", "g", "h", "i", "j", "k"]}
> ---
> {:i=>4}
> {:before=>["a", "c", "e", "g", "h", "i", "j", "k"]}
> {:after=>["a", "c", "e", "g", "i", "j", "k"]}
> ---
> {:i=>5}
> {:before=>["a", "c", "e", "g", "i", "j", "k"]}
> {:after=>["a", "c", "e", "g", "i", "k"]}
> ---
> {:i=>6}
> {:before=>["a", "c", "e", "g", "i", "k"]}
> {:after=>["a", "c", "e", "g", "i", "k"]}
> ---
> {:i=>7}
> {:before=>["a", "c", "e", "g", "i", "k"]}
> {:after=>["a", "c", "e", "g", "i", "k"]}
> ---
> {:i=>8}
> {:before=>["a", "c", "e", "g", "i", "k"]}
> {:after=>["a", "c", "e", "g", "i", "k"]}
> ---
> {:i=>9}
> {:before=>["a", "c", "e", "g", "i", "k"]}
> {:after=>["a", "c", "e", "g", "i", "k"]}
> ---
> {:i=>10}
> {:before=>["a", "c", "e", "g", "i", "k"]}
> {:after=>["a", "c", "e", "g", "i", "k"]}
> ---
> {:i=>11}
> {:before=>["a", "c", "e", "g", "i", "k"]}
> {:after=>["a", "c", "e", "g", "i", "k"]}
>
> look carefully at what's happening for i >= 6.
>
> the indexes map only by accident since each delete modifies the
> mapping in the array (size reduced by one after each delete)
>
> a @http://codeforpeople.com/
> --
> we can deny everything, except that we have the possibility of being
> better. simply reflect on that.
> h.h. the 14th dalai lama

Oops...I really should have noticed that. In a hurry, I guess. I'll
vote for:

a = %w(a b c d e f g h i j k)
1.upto(a.size/2) {|i| a.delete_at i}

as the accidentally obfuscated solution of the day.