Here we are talking about filtering list items again :). I got two comment suggesting the use of yield return.

James Curran said:

Don’t build a new list if you don’t have to.

private static IEnumerable EvenSlicker_FilterPositiveItems(IEnumerable t)

{

foreach(int n in t)

if (n > 0)

yield return n;

}

The advantage is if you try using the method this this:

foreach(int n in FilterPositiveItems(myList) {…}

Your way is O(2N) while mine is O(N)

Hi all

I was into filtering items lately and I have decided to write about some of the techniques out there starting with the old

The good old Foreach

Well we have all used this before once you get a list in your hands just iterate through all the items and select the ones you want:

   1: private static List<int> TheOld_FilterPositiveItems(List<int> t)

   2: {

   3:     List<int> ret = new List<int>();

   4:     foreach (int i in t)

   5:     {

   6:         if (i > 0)

   7:         {

   8:             ret.Add(i);

   9:         }

  10:     }

  11:     return ret;

  12: }

I hope you are not using this method. As there are other good methods like this one:

Hi

A while back I wrote an article about How to sort data by manipulating the view only, This article will handle filtering the data without changing it.

I had a large collection that I needed to display and allow the user to filter it using many parameters. After searching for a while I found a very elegant solution:

What is a Predicate

what are predicates? I will Quote

Represents the method that defines a set of criteria and determines whether the specified object meets those criteria.

You can read more about it here.

Defining a Predicate

A predicate Is a template so you will have to specify the type for instance: