#153 – Returning a Subset of Array Elements Matching a Particular Criteria

Because System.Array implements the IEnumerable interface and because LINQ extends IEnumerable, you can use the IEnumerable.Where method on arrays to find a subset of elements that match a particular criteria.

The Where method accepts a delegate to a function that takes a single element of the same type as the array and returns a boolean value, indicating whether a match is found.  Where returns an IEnumerable collection, which can be iterated on to get the elements in the subset.

Here’s an example, finding the set of passing scores in a set of scores.

            int[] scores = { 89, 98, 72, 100, 68 };

            // Count number of passing grades
            int numPassed = scores.Where((Func<int,bool>)IsPassingGrade).Count();

Here’s the implementation of IsPassingGrade.

        static bool IsPassingGrade(int score)
            return (score >= 75);

You can avoid defining a separate function by using a lamba expression.

            int numPassed = scores.Where(s => s >= 75).Count();

Similar to Array.FindAll.