note BrowserUk <blockquote><i>Also not to be excluded entirely is ... uhh ... an array of integers that is searched sequentially each time. </i></blockquote> <p>That is a surprise winner for my 'Worst Advice of the Month (January, 2013)' prize. <blockquote><i>... set up a few short test-runs ...</i></blockquote> <p>I'd suggest you take your own advice before doling it out to others. <P><b>NB: The following uses 1/10 the number of values and 1/10 the number of lookups than the tests above for arrays, hashes and bit vectors, because it takes so long to complete.</b>:<code> @a = map $_*20, 1 .. 1e4;; say total_size \@a;; 320176 $found=0; say time; for my $tgt ( 1 .. 20e4 ) { $tgt == $_ and ++$found and last for @a; }; say time; say $found;; 1359149323.02034 1359149541.80419 10000 </code> <p>Using that as the basis for estimation, the total size will be 3.2MB -- 12 times that required by the bitvector solution. <P>And the lookups that took hashes 1 second; arrays 2/5ths of a second and bitvectors 1/3rd of a second; would take: <b>25 days!</b> <p>It is really hard to see any circumstance when this would be a viable solution. <div class="pmsig"><div class="pmsig-171588"> <hr /> <font size=1 > <div>With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'</div> <div>Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.</div> <div>"Science is about questioning the status quo. Questioning authority". </div> <div>In the absence of evidence, opinion is indistinguishable from prejudice. </div> </font> </div></div>  1015388 1015401