note merlyn <blockquote><i> However, loading the same 1 million integers into a hash as keys, with undef as the value requires 95 MB! </i></blockquote> I stopped reading there. I don't see your point. Besides storing all the data, you now have a meta-data structure that can tell you rather rapidly if $x is a member of this set you've created, as well as associate another scalar with each of those million keys! <p> You've got a lot more information than what you started with. You're not merely storing the keys. <p> If your complaint is that you want to be able to just store the keys, then yes, a hash was a bad choice, as you go on to point out. <p> But don't fault Perl's hash structure. It's very efficient for the task at hand. <div class="pmsig"><div class="pmsig-9073"> <p>-- [http://www.stonehenge.com/merlyn/|Randal L. Schwartz, Perl hacker] <br> Be sure to read [id://205373|my standard disclaimer] if this is a reply.</p> </div></div> 308947 308947