C＃从列表中删除重复项<string[]>

Question

I got a lot of data from a database, which are results from a search function. Now I've a List<string[]> which has duplicated elements of type string[] . The string[] in the list are the search results.

I know that every new created array has a different instance so i can't use MyListOfArrays.Distinct().ToList() .

Maybe it's a very basic question...

My question is, are there any functions built in to remove a duplicated string[] form the List<string[]> ? Or do I have to write it by my selfe?

Thank you

Answer 1

You can use distinct method with custom equalityComparer

    IEnumerable<string[]> distinct = inputStringArrayList.Distinct(new EqualityComparer());

EqualityComparer

class EqualityComparer : IEqualityComparer<string[]>
{
    public bool Equals(string[] x, string[] y)
    {
        if (x.Length != y.Length)
        {
            return false;
        }
        if (x.Where((t, i) => t != y[i]).Any())
        {
            return false;
        }
        return true;
    }

    public int GetHashCode(string[] obj)
    {
        return obj.GetHashCode(); 
    }
}

Alternative Equals Method

public bool Equals(string[] x, string[] y)
{
    return x.SequenceEqual(y);
}

Here I am assuming you are having exact same string arrays with same content at same index.

Correction from Matthew Watson

public int GetHashCode(string[] obj)
        {
            if (obj == null)
                return 0;

            int hash = 17;

            unchecked
            {
                foreach (string s in obj)
                    hash = hash*23 + ((s == null) ? 0 : s.GetHashCode());
            }

            return hash;
        }

Answer 2

I have corrected the answer from @Muctadir Dinar.

(He deserves credit for the answer - I am just correcting it and providing a complete test program):

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

namespace Demo
{
    sealed class EqualityComparer: IEqualityComparer<string[]>
    {
        public bool Equals(string[] x, string[] y)
        {
            if (ReferenceEquals(x, y))
                return true;

            if (x == null || y == null)
                return false;

            return x.SequenceEqual(y);
        }

        public int GetHashCode(string[] obj)
        {
            if (obj == null)
                return 0;

            int hash = 17;

            unchecked
            {
                foreach (string s in obj)
                    hash = hash*23 + ((s == null) ? 0 : s.GetHashCode());
            }

            return hash;
        }
    }

    class Program
    {
        private void run()
        {
            var list = new List<string[]>
            {
                strings(1, 10), 
                strings(2, 10), 
                strings(3, 10), 
                strings(2, 10), 
                strings(4, 10)
            };

            dump(list);
            Console.WriteLine();

            var result = list.Distinct(new EqualityComparer());
            dump(result);
        }

        static void dump(IEnumerable<string[]> list)
        {
            foreach (var array in list)
                Console.WriteLine(string.Join(",", array));
        }

        static string[] strings(int start, int count)
        {
            return Enumerable.Range(start, count)
                .Select(element => element.ToString())
                .ToArray();
        }

        static void Main(string[] args)
        {
            new Program().run();
        }
    }
}

Answer 3

A simple and not very efficient approach would be to use string.Join on the string[] :

list = list
.GroupBy(strArr => string.Join("|", strArr))
.Select(g => g.First())
.ToList();