C# FindAll VS Where Speed

c# performance where findall
Dested picture Dested · Feb 14, 2010 · Viewed 24.7k times · Source

Anyone know any speed differences between Where and FindAll on List. I know Where is part of IEnumerable and FindAll is part of List, I'm just curious what's faster.

Answer

jrista picture jrista · Feb 14, 2010

The FindAll method of the List<T> class actually constructs a new list object, and adds results to it. The Where extension method for IEnumerable<T> will simply iterate over an existing list and yield an enumeration of the matching results without creating or adding anything (other than the enumerator itself.)

Given a small set, the two would likely perform comparably. However, given a larger set, Where should outperform FindAll, as the new List created to contain the results will have to dynamically grow to contain additional results. Memory usage of FindAll will also start to grow exponentially as the number of matching results increases, where as Where should have constant minimal memory usage (in and of itself...excluding whatever you do with the results.)

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