From: Mike Stok <mike@...>
Date: 2002-09-11T03:35:05+09:00
Subject: Re: Multi-level sort idiom?

In article <1031682194.811634@cswreg.cos.agilent.com>, Brett Williams wrote:
> Let's say I have an array, each element of which is a 2-dimensional array 
> of ints.
> 
> I want to sort with the first element in the 2D array taking precedence, 
> but using the second as a tiebreaker.
> 
> So far, I haven't come up with a nice idiom that doesn't seem a bit kludgy:
> What I tried was to do something like:
> x.sort {|a,b| a[0]<=>b[0] || a[1]<=>b[1]}
> but 0 is not false in Ruby so this doesn't work.
> 
> x.sort {|a,b| 2*(a[0]<=>b[0]) + (a[1]<=>b[1])}
> works, but is non-intuitive and not pretty.
> 
> Does anyone have a nice clean rubyesque idiom for this?

You can use Numeric's nonzero? e.g.

  x = [[5, 1], [3, 2], [3, 3], [1, 5]]
  x.sort { |a, b| (a[0] <=> b[0]).nonzero? || a[1] <=> b[1] }

    => [[1, 5], [3, 2], [3, 3], [5, 1]]

Hope this helps,

Mike

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