Generic list FindAll() vs. foreach


I'm looking through a generic list to find items based on a certain parameter.

In General, what would be the best and fastest implementation?
1. Looping through each item in the list and saving each match to a new list and returning that

foreach(string s in list)
    if(s == "match")

return newList;

2. Using the FindAll method and passing it a delegate.

newList = list.FindAll(delegate(string s){return s == "match";});

Don't they both run in ~ O(N)? What would be the best practice here?

Regards, Jonathan

7/29/2014 4:47:40 PM

Accepted Answer

You should definitely use the FindAll method, or the equivalent LINQ method. Also, consider using the more concise lambda instead of your delegate if you can (requires C# 3.0):

var list = new List<string>();
var newList = list.FindAll(s => s.Equals("match"));
6/9/2011 11:33:14 AM

I would use the FindAll method in this case, as it is more concise, and IMO, has easier readability.

You are right that they are pretty much going to both perform in O(N) time, although the foreach statement should be slightly faster given it doesn't have to perform a delegate invocation (delegates incur a slight overhead as opposed to directly calling methods).

I have to stress how insignificant this difference is, it's more than likely never going to make a difference unless you are doing a massive number of operations on a massive list.

As always, test to see where the bottlenecks are and act appropriately.

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