Sorting and merging a set of numbers and ranges

gistfile1.rb

postcodes = [2000, 3000..3004, 3005, 3010..3020, 3015..3025, 4000..4020, 4010]

postcodes.map do |number_or_range|
  if number_or_range.is_a? Numeric
    (number_or_range..number_or_range)
  elsif number_or_range.is_a? Range
    number_or_range if number_or_range.count > 0
  end
end.compact.sort_by(&:begin).inject([]) do |ranges, range|
  ranges.tap do
    if ranges.last and (ranges.last.include? range.begin or ranges.last.include? range.begin - 1)
      unless ranges.last.include? range.end
        ranges[-1] = (ranges.last.begin..range.end)
      end
    else
      ranges << range
    end
  end
end

# => [2000..2000, 3000..3005, 3010..3025, 4000..4020]