From: "Iñaki Baz Castillo" <ibc@...>
Date: 2011-07-01T19:52:59+09:00
Subject: How to order Structs based on two fields

Hi, I've a struct like this:

  KK = Struct.new(:a,:b)

and some entries in an array:

  kk1=KK.new(0,10)
  #<struct KK a=0, b=10>

  kk2=KK.new(0,5)
  <struct KK a=0, b=5>

  kk3=KK.new(2,0)
  #<struct KK a=2, b=0>

  kk4 = KK.new(2,5)
  #<struct KK a=2, b=5>

  array = [kk3, kk2, kk1, kk4]


I need to order the array based:
- Elements with minor :a must be first.
- If two elements have same :a, then order based on higher :b.

The result should be:

  [kk1, kk2, kk4, kk3]


I expected that the following could work:

  array.sort_by{|entry| entry.a or entry.b}

but it generates:

   [kk1, kk2, kk3, kk4]

so obviously it does not work. I'm not very used to Enumerable.sort_by
method, any tip please?

Thanks a lot.

-- 
Iñaki Baz Castillo
<ibc@aliax.net>