From: Robert Klemme <shortcutter@...>
Date: 2006-05-06T04:58:40+09:00
Subject: Re: Finding an interval in a sorted array?

2006/5/5, Bil Kleb <Bil.Kleb@nasa.gov>:
> Hello,
>
> Surely there is a way to find an interval in a sorted array
> without resorting to indices?  (I'm drawing a blank.)
>
>   require 'test/unit'
>
>   class Array
>     def interval_containing( x )
>       # elegant code goes here
>     end
>   end
>
>   class TestIntervalFinder < Test::Unit::TestCase
>     def test_finds_intervals
>       data = [ 0, 1, 2 ].sort
>       assert_equal [0],   data.interval_containing(-0.2)
>       assert_equal [0],   data.interval_containing( 0.0)
>       assert_equal [0,1], data.interval_containing( 0.5)
>       assert_equal [1],   data.interval_containing( 1.0)
>       assert_equal [1,2], data.interval_containing( 1.6)
>       assert_equal [2],   data.interval_containing( 2.0)
>       assert_equal [2],   data.interval_containing( 5.0)
>     end
>   end

Solutions - of course with inject:

module Enumerable
  def f1(x)
    [inject(nil) {|a,b| return [a,b] if (a||x)<=x && b>x; b}, nil]
  end


  def f2(x)
    inject {|a,b| return [a,b] if a<=x && b>x; b}
    nil
  end
end

irb(main):015:0> a=[0,1,2]
=> [0, 1, 2]
irb(main):016:0> a.f1 0.2
=> [0, 1]
irb(main):017:0> a.f2 0.2
=> [0, 1]
irb(main):018:0> a.f1 0
=> [0, 1]
irb(main):019:0> a.f1 -1
=> [nil, 0]
irb(main):020:0> a.f1 10
=> [2, nil]

Kind regards

robert


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