From: Michael Fellinger <m.fellinger@...>
Date: 2009-03-02T21:26:12+09:00
Subject: Re: how to group visitors using hours

On Mon, Mar 2, 2009 at 9:12 PM, Ayeye Brazov <brazovayeye@yahoo.com> wrote:
> Hi,
>
> I've got this problem, I have a Visitor class that keep tracks
> of visitors. Each visitor has "created_at" field.
> I'd like to group them by hours using "created_at"
>
> I came up with this solution, but I'm not very happy about it...
>
> First, I create a list having ["yy-mm-dd hh",visitor.id], with
>
>    list = visitors.map{|i| [i.created_at.strftime("%Y-%m-%d %H"),
> i.id]}
>
> Then, I group each visitor depending on the hours using an Hash
>
>   hs= {}
>    for l in list
>      if hs.has_key?(l.first)
>        hs[l.first] << l.second # Use the hour as index, and append the
> visitor id
>      else
>        hs[l.first] = [l.second]
>      end
>    end
>
> The result is a Hash hs, and I can use it to get the visitors
> given a certain hour.
>
> However, I'm sure there's a better way of doing it, especially if
> I'd like to group visitors for "months" or "years"
>
> Any suggestions please?!
> thanks
> b.
> --
> Posted via http://www.ruby-forum.com/.
>
>

require 'pp'

class Visitor
  attr_accessor :created_at

  def initialize(time)
    @created_at = time
  end
end

visitors = Array.new(10){ Visitor.new(Time.at(rand(2e9))) }

pp visitors.group_by{|v| v.created_at.hour }
{6=>
  [#<Visitor:0xb7bc034c @created_at=Tue Jul 04 06:22:51 +0900 1978>,
   #<Visitor:0xb7bc00a4 @created_at=Thu Jul 26 06:27:32 +0900 1979>],
 18=>
  [#<Visitor:0xb7bc0194 @created_at=Wed Jun 27 18:31:17 +0900 2018>,
   #<Visitor:0xb7bbffdc @created_at=Sun Oct 03 18:37:50 +0900 1993>],
 13=>[#<Visitor:0xb7bc0108 @created_at=Wed Feb 10 13:20:34 +0900 2027>],
 2=>
  [#<Visitor:0xb7bc0158 @created_at=Fri Jan 10 02:22:01 +0900 2003>,
   #<Visitor:0xb7bc0054 @created_at=Sun May 30 02:15:58 +0900 1993>],
 9=>[#<Visitor:0xb7bbff8c @created_at=Tue Oct 05 09:32:10 +0900 2032>],
 4=>[#<Visitor:0xb7bc0388 @created_at=Mon May 01 04:03:29 +0900 2006>],
 10=>[#<Visitor:0xb7bc002c @created_at=Mon Jun 27 10:28:29 +0900 1994>]}

^ manveru