From: dblack@...
Date: 2005-12-14T05:31:33+09:00
Subject: Re: Array.invert

--8323328-641301970-1134505886=:30520
Content-Type: MULTIPART/MIXED; BOUNDARY="8323328-641301970-1134505886=:30520"

  This message is in MIME format.  The first part should be readable text,
  while the remaining parts are likely unreadable without MIME-aware tools.

--8323328-641301970-1134505886=:30520
Content-Type: TEXT/PLAIN; charset=X-UNKNOWN; format=flowed
Content-Transfer-Encoding: QUOTED-PRINTABLE

Hi --

On Wed, 14 Dec 2005, Simon Kr=C3=B6ger wrote:

> Christer Nilsson wrote:
>> Kroeger, Simon (ext) wrote:
>>=20
>>> Hi Christer,
>>>=20
>>> don't take this to serious:
>>>=20
>>> a =3D [[1,3],[1,4,5]]
>>> p (0...a.size).zip(a).inject([]){|s, b| b[1].each{|i| (s[i] ||=3D []) <=
<
>>> b[0]}; s}
>>>=20
>>> =3D> [nil, [0, 1], nil, [0], [1], [1]]
>>>=20
>>> cheers
>>>=20
>>> Simon
>>=20
>>=20
>> Ruby is so fun, it's impossible to be serious :-)
>>=20
>> a.invert works but not a.invert.invert
>>=20
>> Can you fix that in your amazing oneliner ?
>> Clue: nil.each is the bummer.
>>=20
>> Christer
>
> rofl!
>
> i will give you two:
>
> class Array
>  def invert
>    zip([*(0...size)]).inject([]){|s, b| (b.first || []).each{|i| (s[i] ||=
=3D=20
> []) << b.last}; s}
>  end
> end

You could also do: b.first.to_a, which will be [] for nil and self if
b.first is an array.


David

--=20
David A. Black
dblack@wobblini.net

"Ruby for Rails", forthcoming from Manning Publications, April 2006!
--8323328-641301970-1134505886=:30520--
--8323328-641301970-1134505886=:30520--