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copied!<p>There is a presupposition here, that the most efficient way to do a lot of "Does the array contain X?" checks is to convert the array to a hash. Efficiency depends on the scarce resource, often time but sometimes space and sometimes programmer effort. You are at least doubling the memory consumed by keeping a list and a hash of the the list around simultaneously. Plus you're writing more original code that you'll need to test, document, etc.</p> <p>As an alternative, look at the List::MoreUtils module, specifically the functions <code>any()</code>, <code>none()</code>, <code>true()</code> and <code>false()</code>. They all take a block as the conditional and a list as the argument, similar to <code>map()</code> and <code>grep()</code>:</p> <p><code>print "At least one value undefined" if any { !defined($_) } @list;</code></p> <p>I ran a quick test, loading in half of /usr/share/dict/words to an array (25000 words), then looking for eleven words selected from across the whole dictionary (every 5000th word) in the array, using both the array-to-hash method and the <code>any()</code> function from List::MoreUtils.</p> <p>On Perl 5.8.8 built from source, the array-to-hash method runs almost 1100x faster than the <code>any()</code> method (1300x faster under Ubuntu 6.06's packaged Perl 5.8.7.)</p> <p>That's not the full story however - the array-to-hash conversion takes about 0.04 seconds which in this case kills the time efficiency of array-to-hash method to 1.5x-2x faster than the <code>any()</code> method. Still good, but not nearly as stellar.</p> <p>My gut feeling is that the array-to-hash method is going to beat <code>any()</code> in most cases, but I'd feel a whole lot better if I had some more solid metrics (lots of test cases, decent statistical analyses, maybe some big-O algorithmic analysis of each method, etc.) Depending on your needs, List::MoreUtils may be a better solution; it's certainly more flexible and requires less coding. Remember, premature optimization is a sin... :)</p>

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