file.rb

# Title is an active record model
titles = Title.all.each { |title| title.some_attribute = Random.new_seed }.sort_by { |title| title.some_attribute }

Your code works, the only problem is : your loop 2 times on the array.
You may want to avoid it with this tricks:

# Ensure that item has some_attribute value and return this value
def ensure_item_some_attr item
  item.some_attribute ||= Random.new_seed
end
# Sort items, and at the same time, set value to items that don't have
titles = Title.all.sort {|x, y| ensure_item_some_attr(x) <=> ensure_item_some_attr(y) }

But it's really not a nice code, not really explicit ...