如何在一个列表中合并两个列表而不采取联合或加入 C # 而不重复？

Question

italic Problem: We have the Student class with a single field Name (string).Build a function that takes as input two student lists and returns a single list that contains elements of two input lists, excluding those with duplicate names. italic Here is my code:

using System;
using System.Collections.Generic;

namespace ExerciseGeneric(listA, listB)
{
    class Program
    {
        static void Main(string[] args)
        {
            List<string> ListA = new List<string>
      { 
         "James",
         "Jon",
         "Mark",
         "Jey",
         "Sara",
      };

            List<string> ListB = new List<string>
      {
         "Peter",
         "Parker",
         "Bond",
         "Sara"
      };

          

          
            List<string> ListResult = new List<string>();

            foreach (var item in ListA)
            {
                ListResult.Add(item);
            }

            foreach (var item in ListB)
            {
                ListResult.Add(item);
            }
            for (var i = 0; i < ListResult.Count; ++i)
                {
                    for (var j = i + 1; j < ListResult.Count; ++j)
                    {
                        
                        if (ListResult[i] == ListResult[j])
                        {
                            ListResult.Remove(j, 1);
                    }
                    break;
                }

            foreach (var result in ListResult)
            {
                Console.WriteLine("ListResult : " + result);
            }


            }
        }
    }
}     

Answer 1

If you want to remove duplicates I suggest using set , eg HashSet<string> :

   HashSet<string> combined = new HashSet<string>(ListA);

   combined.UnionWith(ListB);

   List<string> ListResult = new List<string>(combined.Count);

   foreach (string item in combined)
     ListResult.Add(item);

Or if using UnionWith is cheating :

   HashSet<string> combined = new HashSet<string>();  

   List<string> ListResult = new List<string>();

   foreach (string item in ListA)
     if (combined.Add(item)) // if item is unique (i.e. added to the set)
       ListResult.Add(item); // we add it into the list as well  

   foreach (string item in ListB)
     if (combined.Add(item))
       ListResult.Add(item);   

Finally, if everything but ListResult is prohibited (disclamer: List<T> is not very good choice for Contains ):

   List<string> ListResult = new List<string>();

   foreach (string item in ListA)
     if (!ListResult.Contains(item))
       ListResult.Add(item);

   foreach (string item in ListB)
     if (!ListResult.Contains(item))
       ListResult.Add(item);

you can easily turn foreach loop into for one:

   for (int i = 0; i < ListA.Count; ++i) {
     string item = listA[i];

     if (!ListResult.Contains(item))
       ListResult.Add(item);
   }

   for (int i = 0; i < ListB.Count; ++i) {
     string item = listB[i];

     if (!ListResult.Contains(item))
       ListResult.Add(item);
   }

Answer 2

You can use the AddRange method to combine the two lists then use Distinct to get rid of the duplicates.

List<string> namesA = new List<string>() { "A", "B", "C" };
List<string> namesB = new List<string>() { "D", "A", "B" };

namesA.AddRange(namesB);
List<string> combined = namesA.Distinct().ToList();

combined.ForEach(x => Console.WriteLine(x));

prints:

A
B
C
D

You can also do the following.. this keeps the original lists unmodified.

List<string> namesA = new List<string>() { "A", "B", "C" };
List<string> namesB = new List<string>() { "D", "A", "B" };
List<string> combined = new List<string>();

combined.AddRange(namesA);
combined.AddRange(namesB);
combined = combined.Distinct().ToList();

combined.ForEach(x => Console.WriteLine(x));

Answer 3

Adding to the HashSet answer by Dmitry, assuming that you are only not allowed to use Join and Union I think it another alternative is to use the .Distinct() method in System.Linq .

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

public class Program
{
    public static void Main()
    {
        List<string> ListA = new List<string>
        { 
            "James",
            "Jon",
            "Mark",
            "Jey",
            "Sara",
        };

        List<string> ListB = new List<string>
        {
            "Peter",
            "Parker",
            "Bond",
            "Sara"
        };
        
        List<string> ListResult = new List<string>();

        foreach (var item in ListA)
        {
            ListResult.Add(item);
        }

        foreach (var item in ListB)
        {
            ListResult.Add(item);
        }

        ListResult = ListResult.Distinct()
            .ToList();
        
        foreach(var item in ListResult)
        {
            Console.WriteLine(item);    
        }
    }
}

Albeit, this answer is going to be slower compared to using HashSet.

Answer 4

Using Union seems to be the best option here, but if you cant:

ListA.Concat(ListB).Distinct();