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    <p>Matt's answer, getting the keys first, separately is the right way to go. Yes, there'll be some redundancy - but it will work. I'd take a working program which is easy to debug and maintain over an efficient program which either won't work or is hard to maintain any day. </p> <p>Don't forget that if you make <code>MovieUser</code> a reference type, the array will only be the size of as many references as you've got users - that's pretty small. A million users will only take up 4MB or 8MB on x64. How many users have you really got?</p> <p>Your code should therefore be something like:</p> <pre><code>IEnumerable&lt;MovieUser&gt; users = RetrieveUsers(); IDictionary&lt;MovieUser, float&gt; questions = new Dictionary&lt;MovieUser, float&gt;(); foreach (MovieUser user in users) { questions[user] = RetrieveGuess(user); } </code></pre> <p>If you're using .NET 3.5 (and can therefore use LINQ), it's even easier:</p> <pre><code>IDictionary&lt;MovieUser, float&gt; questions = RetrieveUsers.ToDictionary(user =&gt; user, user =&gt; RetrieveGuess(user)); </code></pre> <p>Note that if <code>RetrieveUsers()</code> can stream the list of users from its source (e.g. a file) then it will be efficient anyway, as you never need to know about more than one of them at a time while you're populating the dictionary.</p> <p>A few comments on the rest of your code:</p> <ul> <li>Code conventions matter. Capitalise the names of your types and methods to fit in with other .NET code.</li> <li>You're not calling <code>Dispose</code> on the <code>IEnumerator&lt;T&gt;</code> produced by the call to <code>GetEnumerator</code>. If you just use <code>foreach</code> your code will be simpler <em>and</em> safer.</li> <li><code>MovieUser</code> should almost certainly be a class. Do you have a genuinely good reason for making it a struct?</li> </ul>
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    1. COI really appreciate the insight - I am very new to .NET in general, coming from a C++ background, so this would explain my unconventional thinking. Comments like these are great for my learning.
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      1. USDavid Ackerman
 

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