From: Gregory Brown <gregory.t.brown@...>
Date: 2009-07-14T22:27:59+09:00
Subject: Elegant solution for inverting zip?

Hi folks,

I came across something I thought should have an obvious answer and
came up blank.  I'm hoping folks could give me a nice solution to this
problem.

Given the output below:

>> a = [1,2,3,4].zip([5,6,7,8])
=> [[1, 5], [2, 6], [3, 7], [4, 8]]


I'd like to recover the original two arrays, something like

unzip(a) #=> [[1,2,3,4],[5,6,7,8]]

The best ordinary solution I could come up with was this:

b = a.each_with_object([[],[]]) do |pair, memo|
  memo[0] << pair[0]
  memo[1] << pair[1]
end

Shorter, but perhaps weirder, is:

require "matrix"
b = Matrix[*a].column_vectors.map(&:to_a)

Although either of these solutions are likely good enough for my
needs, neither feel natural to me.  Anyone have something better?

-greg