GroupJoin to separate lists

CSharp · Console

/Program.cs

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

namespace ConsoleApplication1
{
    class Parent
    {
        public string ParentName { get; set; }
        public IEnumerable<string> ChildNames { get; set; }
    }

    class Child
    {
        public string ParentName { get; set; }
        public string ChildName { get; set; }
    }

    public class Program
    {
        public static void Main(string[] args)
        {
            var parents = new List<Parent>()
            {
                new Parent() {ParentName = "Lee"},
                new Parent() {ParentName = "Bob"},
                new Parent() {ParentName = "Tom"}
            };

            var children = new List<Child>()
            {
                new Child() {ParentName = "Lee", ChildName = "A"},
                new Child() {ParentName = "Tom", ChildName = "B"},
                new Child() {ParentName = "Tom", ChildName = "C"}
            };

            ///////////////////////////////////////////////
            // Technique #1:
            foreach (var parent in parents)
            {
                var p = parent; // to avoid foreach closure side-effects
                p.ChildNames = children.Where(c => c.ParentName == p.ParentName).Select(c => c.ChildName);
            }
            Display("Technique #1:", parents);
            ///////////////////////////////////////////////


            ///////////////////////////////////////////////
            // Technique #2:			
            var parentChildPairs =
                from p in parents
                join c in children on p.ParentName equals c.ParentName into childList
                select new { Parent = p, ChildrenNames = childList.Select(c => c.ChildName) };

            foreach (var dzp in parentChildPairs)
            {
                var p = dzp.Parent;
                var c = dzp.ChildrenNames; // to avoid foreach closure side-effects
                p.ChildNames = c;
            }
            Display("Technique #2:", parentChildPairs.Select(p => p.Parent));
            ///////////////////////////////////////////////
			
			
			///////////////////////////////////////////////
            // Technique #3:
            parents.ForEach(p => p.ChildNames = children.Where(c => c.ParentName == p.ParentName).Select(c => c.ChildName).ToList());
            Display("Technique #3:", parents);
            ///////////////////////////////////////////////

			
            ///////////////////////////////////////////////
            // Technique #4:
            var clu = children.ToLookup(c => c.ParentName, c => c.ChildName);
            parents.ForEach(p => p.ChildNames = clu[p.ParentName]);
            Display("Technique #4:", parents);
            ///////////////////////////////////////////////
			
        }

        static void Display(string message, IEnumerable<Parent> parents)
        {
            Console.WriteLine(message);
            foreach (var p in parents)
            {
                var childNames = string.Join(",", p.ChildNames);
                Console.WriteLine("Parent = {0}, Children = {1}", p.ParentName, childNames);
            }
            Console.WriteLine("");
        }
    }
}