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POTake & remove elements from collection
 

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    <p>What's the most performant way to remove n elements from a collection and add those removed n elements to an already existing, different, collection?</p> <p>Currently I've got this:</p> <pre><code>var entries = collection.Take(5).ToList(); foreach(var entry in entries) collection.Remove(entry); otherCollection.AddRange(entries); </code></pre> <p>However, this doesn't look performant at all to me (<em>multiple</em> linear algorithms instead of only one).</p> <p>A possible solution may of course change the collection implementation - as long as the following requirements are met:</p> <ul> <li><code>otherCollection</code> must implement <code>IEnumerable&lt;T&gt;</code>, it is currently of type <code>List&lt;T&gt;</code></li> <li><code>collection</code> must implement <code>ICollection&lt;T&gt;</code>, it is currently of type <code>LinkedList&lt;T&gt;</code></li> </ul> <p>Hint: entries do not necessarily implement <code>Equals()</code> or <code>GetHashCode()</code>.</p> <p>What's the most performant way to reach my goal?</p> <hr> <p>As it has been obviously too hard to understand my performance considerations, here once more my code example:</p> <pre><code>var entries = collection.Take(1000).ToList(); // 1000 steps foreach(var entry in entries) // 1000 * 1 steps (as Remove finds the element always immediately at the beginning) collection.Remove(entry); otherCollection.AddRange(entries); // another 1000 steps </code></pre> <p>= 3000 steps in total => I want to reduce it to a single 1000 steps.</p>
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    1. COYou always have a linear search with a O(n) operation, there is nothing better with a collection.
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      1. USTim Schmelter
    2. COI think the collection has a RemoveAll(collection.Take(5))
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      1. USJ. van Langen
    3. CO@TimSchmelter: It's not about collection or non-linear search. It's about how to avoid *multiple* O(n) operations. See my code sample!
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