ranges_of_contiguous

enumerable_extensions.rb

module Enumerable
  # Returns an array of arrays, each inner array containing a cluster of contiguous elements from
  # self.
  #
  # [-1, 0, 1, 3, 4, 7, 8].clusters_of_contiguous
  # => [[-1, 0, 1], [3, 4], [7, 8]]
  #
  # Based off of Enumerable#cluster (from facets gem)
  #
  def clusters_of_contiguous
    clusters = []
    each do |element|
      cluster = clusters.last
      if cluster && cluster.last.succ == element
        cluster << element
      else
        clusters << [element]
      end
    end
    clusters
  end

  # Returns an array of ranges, each range representing a range of contiguous elements from self.
  #
  # [-1, 0, 1, 3, 4, 7, 8].ranges_of_contiguous
  # => [-1..1, 3..4, 7..8]
  #
  def ranges_of_contiguous
    ranges = []
    each do |element|
      range = ranges.last
      if range && range.end.succ == element
        ranges[-1] = (range.begin .. element)
      else
        ranges << (element .. element)
      end
    end
    ranges
  end
end

enumerable_spec.rb

describe Enumerable do
  describe '-1, 0, 1, 3, 4, 7, 8' do
    subject { [-1, 0, 1, 3, 4, 7, 8] }
    its(:clusters_of_contiguous) { should == [[-1, 0, 1], [3, 4], [7, 8]] }
    its(:ranges_of_contiguous)   { should == [ -1..1,      3..4,   7..8] }
  end

  # It doesn't care what the elements are, as long as they are Enumerable (respond_to? :succ)
  describe 'PK, K, 1, 3, 4, 7, 8' do
    subject { [
      GradeLevel.new('PK'),
      GradeLevel.new('K'),
      GradeLevel.new('1'),
      GradeLevel.new('3'),
      GradeLevel.new('4'),
      GradeLevel.new('7'),
      GradeLevel.new('8'),
    ] }
    its(:clusters_of_contiguous) { should == [
      [
        GradeLevel.new('PK'),
        GradeLevel.new('K'),
        GradeLevel.new('1'),
      ],
      [
        GradeLevel.new('3'),
        GradeLevel.new('4'),
      ],
      [
        GradeLevel.new('7'),
        GradeLevel.new('8'),
      ]
    ] }
    its(:ranges_of_contiguous)   { should == [
      (
        GradeLevel.new('PK') ..
        GradeLevel.new('1')
      ),
      (
        GradeLevel.new('3') ..
        GradeLevel.new('4')
      ),
      (
        GradeLevel.new('7') ..
        GradeLevel.new('8')
      )
    ] }
  end
end