Collapse an array of ranges into the union of their ranges

collapse_array_of_ranges.rb

def collapse_array_of_ranges(array)
  # simplify, by sorting on range.begin
  array.sort_by(&:begin).inject([]) do |a, r|
    # compared with last range...
    last_range = a[-1]
    if last_range && last_range.include?(r.begin)
      # ignore range if it is completely inside of last range
      unless(last_range.include?(r.end))
        # this range overlaps last range,
        # thus, pull off last range and merge them
        a.pop
        a.push(last_range.begin..r.end)
      end
    else
      # this range does not intersect last range
      # thus, put it on array
      a.push(r)
    end
    a
  end
end

collapse_array_of_ranges([1..3, 2..4, 2..7])
# => [1..7]
collapse_array_of_ranges([1..3, 2..4, 2..7, 8..9])
# => [1..7, 8..9]
collapse_array_of_ranges([805..827, 326..426, 1..10, 526..715, 708..722, 804..826])
# => [1..10, 326..426, 526..722, 804..827]