Conditional IEnumerable.Select

Utils.cs

public static IEnumerable<TResult> SelectWhere<TSource, TResult>(
            this IEnumerable<TSource> source,
            Func<TSource, TResult> selector,
            Func<TSource, bool> predicate)
        {
            foreach (TSource item in source)
                if (predicate(item))
                    yield return selector(item);
        }