From: Stefan Rusterholz <apeiros@...>
Date: 2009-01-24T19:16:29+09:00
Subject: Re: Sorting array with nils

(RK) Sentinel wrote:
>   def sort categ, column, descending=false
>     d = get_records_for_category categ
>     d = d.sort { |y,x|
>       if descending
>         if x[column].nil?
>           true   # <<<<------------- errors --- yes of course, <=> expectes -1,0,1, not true/false
>         elsif y[column].nil?
>           false   # <<<<------------- errors too, for the same reason
>         else
>           x[column] <=> y[column]
>         end
>       else
>         if x[column].nil?
>           1     # <<<-------------- gives errors --- no, should not
>         elsif y[column].nil?
>           -1
>         else
>           y[column] <=> x[column]
>         end
>       end
>     }
>     return d
>   end

A solution (untested):
class Uncomparable
  def initialize(always_less=true)
    @compare = always_less ? -1 : 1
  end

  def <=>(other)
    Uncomparable === other ? 0 : @compare
  end
end
...
d.sort_by { |row| row[column] || Uncomparable(!descending) }
...

Depending on what end you want the nils, you have to change !descending 
to just descending.

Regards
Stefan
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