From: Robert Klemme <shortcutter@...>
Date: 2008-01-07T03:15:02+09:00
Subject: Re: add rankings to array?

On 06.01.2008 18:30, soprano wrote:
> Is it possible to add rankings to an array (allowing ties):
> 
> Example (rate on points field) - convert
> 
> [
>   { :name => "A", :points => 30 },
>   { :name => "B", :points => 20 },
>   { :name => "C", :points => 10 },
>   { :name => "D", :points => 20 }
> ]
> 
> to
> 
> [
>   [1, { :name => "A", :points => 30 }],
>   [2, { :name => "B", :points => 20 }],
>   [2, { :name => "D", :points => 20 }],
>   [4, { :name => "C", :points => 10 }]
> ]
> 
> How to do this in Ruby?

Preparation:

data = [
   { :name => "A", :points => 30 },
   { :name => "B", :points => 20 },
   { :name => "C", :points => 10 },
   { :name => "D", :points => 20 }
]

Here's one way:

sorted = data.sort_by {|x| -x[:points]}
ranked = sorted.inject([0,1,nil,[]]) do |(rk, cn, lst, arr), x|
   tmp_lst = x[:points]

   if tmp_lst == lst
     cn += 1
   else
     rk += cn
     cn  = 1
   end

   [rk, cn, tmp_lst, arr << [rk, x]]
end.last


And here's another:

hashed = data.inject(Hash.new {|h,k| h[k] = []}) do |ha, x|
   ha[x[:points]] << x
   ha
end
sorted = hashed.sort_by {|k,v| -k}
ranked = sorted.inject([]) do |arr, (k,v)|
   rk = arr.size + 1
   v.each {|x, idx| arr << [rk, x]}
   arr
end


Have fun!

Kind regards

	robert