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    <p>The simplest way is usually the <a href="http://msdn.microsoft.com/en-us/library/bb341406.aspx" rel="noreferrer"><code>Cast</code></a> extension method:</p> <pre><code>IEnumerable&lt;Match&gt; strongMatches = matches.Cast&lt;Match&gt;(); </code></pre> <p>Note that this is deferred and streams its data, so you don't have a full "collection" as such - but it's a perfectly fine data source for LINQ queries.</p> <p><code>Cast</code> is automatically called if you specify a type for the range variable in a query expression:</p> <p>So to convert your query completely:</p> <pre><code>public static int MaxSequence(string str) { return (from Match match in Regex.Matches(str, "H+|T+") select match.Value.Length into matchLength orderby matchLength descending select matchLength).First(); } </code></pre> <p>or</p> <pre><code>public static int MaxSequence(string str) { MatchCollection matches = Regex.Matches(str, "H+|T+"); return matches.Cast&lt;Match&gt;() .Select(match =&gt; match.Value.Length) .OrderByDescending(len =&gt; len) .First(); } </code></pre> <p>In fact, you don't need to call <code>OrderByDescending</code> and then <code>First</code> here - you just want the maximal value, which the <code>Max</code> method gets you. Even better, it lets you specify a projection from a source element type to the value you're trying to find, so you can do without the <code>Select</code> too:</p> <pre><code>public static int MaxSequence(string str) { MatchCollection matches = Regex.Matches(str, "H+|T+"); return matches.Cast&lt;Match&gt;() .Max(match =&gt; match.Value.Length); } </code></pre> <p>If you have a collection which has <em>some</em> elements of the right type but some which may not be, you can use <a href="http://msdn.microsoft.com/en-us/library/bb360913.aspx" rel="noreferrer"><code>OfType</code></a> instead. <code>Cast</code> throws an exception when it encounters an item of the "wrong" type; <code>OfType</code> just skips over it.</p>
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    1. POWhat's the best way to convert non-generic collection to a generic collection?
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    1. USJon Skeet
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    1. COThanks very much! I'm not sure how I missed that method in the documentation, but that's exactly what I was looking for! Also thanks for the tip on using Max()
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