From: Josh Cheek <josh.cheek@...>
Date: 2011-07-01T20:15:00+09:00
Subject: Re: How to order Structs based on two fields

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On Fri, Jul 1, 2011 at 5:55 AM, I=F1aki Baz Castillo <ibc@aliax.net> wrote:

> 2011/7/1 I=F1aki Baz Castillo <ibc@aliax.net>:
> > 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?
>
> Maybe it would be better to use "class KK" rather than an struct, and
> then define <=3D> method for KK class (and include Enumerable module)?
>
> --
> I=F1aki Baz Castillo
> <ibc@aliax.net>
>
>

Structs return classes already (this is why you can inherit from them in th=
e
form `class A < Struct.new(:a,:b)`). You can pass Struct.new a block, and i=
t
will be evaluated within the context of the struct you are creating:


KK =3D Struct.new(:a,:b) do
  def <=3D>(kk)
    if a < kk.a
      -1
    elsif a > kk.a
      1
    else
      kk.b <=3D> b
    end
  end
end

kk1=3DKK.new(0,10)
kk2=3DKK.new(0,5)
kk3=3DKK.new(2,0)
kk4 =3D KK.new(2,5)
array =3D [kk3, kk2, kk1, kk4]


# 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] =3D=3D array.sort # =3D> true

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