From: Wybo Dekker <wybo@...>
Date: 2006-02-05T22:16:54+09:00
Subject: Re: how to vary sort's block?

Thanks all for the very valuable explanations and suggestions. 
I finally came to the conclusion that, for my problem (to do a sort, 
depending on the value of some variable `order'), sort_by is the most 
versatile way. I saved an example for future reference, which may be 
useful for others on the list: 

#!/usr/bin/ruby

class Thing
  attr_reader :name,:amount
  def initialize(name,amount)
    @name,@amount = name,amount
  end
  def list
    puts ['',@name,@amount].join("\t")
  end
end

arr = [
  Thing.new('Johnny',20), Thing.new('Anny',20),
  Thing.new('John',10),   Thing.new('Anny',10),
  Thing.new('John',30),   Thing.new('Anny',30),
]

for order in [:name, :amount]
  puts "by #{order}:"
  arr.sort_by{|x| x.send(order)}.each {|a| a.list}
end

order = :name
puts "by #{order}_length, #{order}, amount:"
arr.sort_by{|x| [ x.send(order).length,
                  x.send(order),
                  x.amount
                ]
}.each {|a| a.list}

PS. Good to see in the definition of arr that the extra comma after the 
last element is not an error anymore.

-- 
Wybo