class TablePrint::Row

def collapse!
  children.each(&:collapse!)  # depth-first. start collapsing from the bottom and work our way up.
  to_absorb = []
  children.each do |group|
    next unless can_absorb?(group)
    to_absorb << group
  end
  to_absorb.each do |absorbable_group|
    absorbable_row = absorbable_group.children.shift
    # missing associations create groups with no rows
    children.delete(absorbable_group) and next unless absorbable_row
    @cells.merge!(absorbable_row.cells)
    i = children.index(absorbable_group)
    children.delete(absorbable_group) if absorbable_group.children.empty?
    insert_children(i, absorbable_row.children) if absorbable_row.children.any?
  end
end