From: Alex Young <alex@...>
Date: 2006-10-17T18:45:23+09:00
Subject: Re: Array.new question

Peter Szinek wrote:
>> a = (0..3).collect{[]} # => [[], [], [], []]
>> a[0][0] = 1
>> a # => [[1], [], [], []]
> 
> Thx!
> 
>>> 2) Is there an idiomatic way to do this (in a generic way, of course):
>>>
>>> some_func(
>>> [1,2,3]
>>> [4,5,6]
>>> [7,8,9] )
>>>
>>> => [ [1,4,7], [2,5,8], [3,6,9] ]
>> [1,2,3].zip([4,5,6],[7,8,9]) # => [[1,4,7], [2,5,8], [3,6,9]]
> 
> Sorry, I did not describe the scenario properly.
> The thing is that I am iterating over an array (of arrays)
> and I don't have the all the arrays at once (the inner arrays are 
> generated on the fly). Let me illustrate it:
> 
> input = [ [1,2,3], [4,5,6], [7,8,9] ]
> result = []
> 
> input.each { |i| do_something_with(result, i) }
> 
> and the result should be
> 
> [ [1,4,7], [2,5,8], [3,6,9] ]
> 
> The question sounds: how is do_something_with implemented?
> I have already implemented it but I don't think so it's a state-of-the 
> art solution ;)
Right...  In that case, how about this:

input.each{|i| i.each_with_index{|x,j| (result[j] ||= []) << x}}

Not sure if it'll play the way you want with variable-length arrays, but 
it puts the right contents in result.

-- 
Alex