From: "Shot (Piotr Szotkowski)" <shot@...>
Date: 2007-12-17T00:05:09+09:00
Subject: Re: An idiomatic way to traverse all pairs in an enumerable?

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Rob Biedenharn:

> On Dec 15, 2007, at 6:03 PM, Shot (Piotr Szotkowski) wrote:

>> In general, I=E2=80=99m looking for an idiomatic way of traversing
>> each possible pair of a given enum=E2=80=99s contents (once).

> http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-list/42671

> You could use the Array#combination code
> posted there either directly or as an example.

Thanks a lot!

In a related field, the above touched some obscure part of my brain
and I recalled the permutation gem: http://permutation.rubyforge.org/

> If you can rely on the ordering of elements
> (your a>=3Db), your code isn't too bad

If I can=E2=80=99t rely on it, I use each_with_index:

each_with_index do |a, i|
  each_with_index do |b, j|
    next if i >=3D j
    # do something with a and b
  end
end

> If you have an enumerable that's not an Array,
> you might have some tweaking to do anyway.

The above each_with_index works quite well for most
(all?) enumerables. :) Thanks again for your reply!

-- Shot
--=20
He's dead, Jim. You take his phaser, I'll get his wallet.

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