From: Gennady Bystritsky <Gennady.Bystritsky@...>
Date: 2006-08-15T07:02:52+09:00
Subject: Re: Consecutive sort on Array of Hashes

> Hi,
> 
> Here my - strange - problem.
> 
> To explain it, let's take the example of football. I 
> construct an array 
> of hashes of the results with team_id, total of pts, number of wins, 
> number of draws and number of defeats such as:
> 
> myArray = Array.new
> myArray << {:team_id=>1, :pts=>5, :w=>0,  :d=>5, :l=>5}
> myArray << {:team_id=>2, :pts=>7, :w=>1,  :d=>4, :l=>5}
> myArray << {:team_id=>3, :pts=>4, :w=>0,  :d=>4, :l=>6}
> myArray << {:team_id=>4, :pts=>6, :w=>1,  :d=>3, :l=>6}
> myArray << {:team_id=>5, :pts=>5, :w=>0,  :d=>5, :l=>5}
> myArray << {:team_id=>6, :pts=>5, :w=>0,  :d=>5, :l=>5}
> myArray << {:team_id=>8, :pts=>10, :w=>2,  :d=>4, :l=>4}
> myArray << {:team_id=>9, :pts=>5, :w=>1,  :d=>2, :l=>7}
> myArray << {:team_id=>10, :pts=>8, :w=>1,  :d=>5, :l=>4}
> myArray << {:team_id=>11, :pts=>9, :w=>2,  :d=>3, :l=>5}
> myArray << {:team_id=>12, :pts=>6, :w=>1,  :d=>3, :l=>6}
> myArray << {:team_id=>13, :pts=>5, :w=>0,  :d=>5, :l=>5}
> 
> Now, from this array, I want to get the table.
> So what I want to do is to sort the array,  first by total of 
> pts, then 
> by number of wins (if 2 teams have the same total of points I 
> put first 
> the team with more wins) and then by number of draws.
> 
> That's how - logically - I would do it anyway. But that does 
> not seem to 
> be the Ruby way. Doing it that way gives me a complete mess.
> 
> No worries, doing it the other way round works (first sort by 
> draw, then 
> wins, then pts)! Here is what I run:
> 
> puts "Team, Pts, W, D, L"
> myArray = myArray.sort { |a,b| b[:d] <=> a[:d]
> 		}.sort { |a,b| b[:w] <=> a[:w]
> 		}.sort { |a,b| b[:pts] <=> a[:pts]
> 		}.each do |row|
> puts "#{row[:team_id]}, #{row[:pts]}, #{row[:w]}, #{row[:d]}, 
> #{row[:l]}"
> end
> 
> Did I say it works? Well almost! Here is my output:
> 
> Team, Pts, W, D, L
> 8, 10, 2, 4, 4
> 11, 9, 2, 3, 5
> 10, 8, 1, 5, 4
> 2, 7, 1, 4, 5
> 4, 6, 1, 3, 6
> 12, 6, 1, 3, 6
> 16, 5, 0, 5, 5
> 1, 5, 0, 5, 5
> 9, 5, 1, 2, 7
> 5, 5, 0, 5, 5
> 6, 5, 0, 5, 5
> 3, 4, 0, 4, 6
> 
> Good news, we kept the correct team_is with the correct result.
> But can anyone explain me what on earth is the line 9, 5, 1, 
> 2, 7 doing 
> there in the middle?
> 
> Thanks for your help!

Each of your sort's just re-arranges the array by the new criteria,
completely unrelated to previous sorts. Why not simply to create an
appropriate criteria for a single sort:

[ DISCLAIMER: Untested code bellow ]

myArray = myArray.sort { |b, a| 
  diff = 0
  [ :pts, :w, :d ].each do |_criteria|
    diff = a[_criteria] - b[_criteria]
    break unless diff.zero?
  end
  diff
}

Or even cooler ;-)

myArray = myArray.sort { |a, b|
  [ :pts, :w, :d ].inject(0) { |_m, _c|
    _m == 0 ? b[_c] - a[_c] : _m
  }
}

Gennady.

> 
> -- 
> Posted via http://www.ruby-forum.com/.
> 
>