Umbraco-CMS/umbraco.MacroEngines.Juno/RazorDynamicNode/ExtensionMethods.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace umbraco.MacroEngines
{
    public static class ExtensionMethods
    {
        public static IEnumerable<TSource> Map<TSource>(
            this IEnumerable<TSource> source,
            Func<TSource, bool> selectorFunction,
            Func<TSource, IEnumerable<TSource>> getChildrenFunction)
        {
            // Add what we have to the stack   
            var flattenedList = source.Where(selectorFunction);
            // Go through the input enumerable looking for children,   
            // and add those if we have them   
            foreach (TSource element in source)
            {
                flattenedList = flattenedList.Concat(getChildrenFunction(element).Map(selectorFunction, getChildrenFunction));
            }
            return flattenedList;
        }
    }
}