从元组列表中删除重复项

Question

我有一个 Tuple<string,string> 对象列表，我想删除重复项，例如，元组 (a,b) 和 (b,a) 被认为是相同的（这些是图的边缘）。这样做的不错方法是什么？

Answer 1

您需要创建一个可以比较元组的比较器，以使项目的顺序无关紧要：

public class UnorderedTupleComparer<T> : IEqualityComparer<Tuple<T, T>>
{
    private IEqualityComparer<T> comparer;
    public UnorderedTupleComparer(IEqualityComparer<T> comparer = null)
    {
        this.comparer = comparer ?? EqualityComparer<T>.Default;
    }

    public bool Equals(Tuple<T, T> x, Tuple<T, T> y)
    {
        return comparer.Equals(x.Item1, y.Item1) && comparer.Equals(x.Item2, y.Item2) ||
                comparer.Equals(x.Item1, y.Item2) && comparer.Equals(x.Item1, y.Item2);
    }

    public int GetHashCode(Tuple<T, T> obj)
    {
        return comparer.GetHashCode(obj.Item1) ^ comparer.GetHashCode(obj.Item2);
    }
}

请注意，哈希码的异或运算是一种无论操作数的顺序如何都会产生相同结果的操作，这使得它在这里是可取的（但不是在大多数哈希码生成算法中，因为它通常是一个 不受欢迎的属性）。至于Equals，只需检查两个可能的配对即可。

一旦你有了，你就可以做到：

var query = data.Distinct(new UnorderedTupleComparer<string>());

Answer 2

您可能需要创建一个实现IEqualityComparer<Tuple<string, string>> 的类：

public class TupleComparer : IEqualityComparer<Tuple<string, string>>
{
    public bool Equals(Tuple<string, string> x, Tuple<string, string> y)
    {

        if (ReferenceEquals(x, y))
        {
            return true;
        }

        if (ReferenceEquals(x, null) || ReferenceEquals(y, null))
        {
            return false;
        }

        if (x.Item1.Equals(y.Item2) && x.Item2.Equals(y.Item1))
        {
            return true;
        }

        return x.Item1.Equals(y.Item1) && x.Item2.Equals(y.Item2);
    }   

    public int GetHashCode(Tuple<string, string> tuple)
    {
        // implementation
    }
}

然后您可以像这样使用Distinct() LINQ 方法：

List<Tuple<string, string>> list = new List<Tuple<string, string>> { Tuple.Create("a", "b"), Tuple.Create("a", "c"), Tuple.Create("b", "a") };
var result = list.Distinct(new TupleComparer());

Answer 3

尝试使用字典并组成一个表示每个元组的键。你有一个不会出现在你的字符串中的字符，你可以用作分隔符吗？我在这个例子中选择了“：”：

static void Main(string[] args)
{
    // original list of data
    var list = new List<Tuple<string, string>> { };
    list.Add(new Tuple<string, string>("a", "b"));
    list.Add(new Tuple<string, string>("b", "a"));

    // dictionary to hold unique tuples
    var dict = new Dictionary<string, Tuple<string, string>>();
    foreach (var item in list)
    {
        var key1 = string.Concat(item.Item1, ":", item.Item2);
        var key2 = string.Concat(item.Item2, ":", item.Item1);

        // if dict doesnt contain tuple, add it.
        if (!dict.ContainsKey(key1) && !dict.ContainsKey(key2))
            dict.Add(key1, item);
    }

    // print unique tuples
    foreach (var item in dict)
    {
        var tuple = item.Value;
        Console.WriteLine(string.Concat(tuple.Item1, ":", tuple.Item2));
    }

    Console.ReadKey();
}

Answer 4

直播代码：https://dotnetfiddle.net/LUErFj

首先对 Tuple 对进行排序，然后进行 Distinct：

using System;
using System.Collections.Generic;

using System.Linq;

public class Program
{
    static List<Tuple<string, string>> myList = new List<Tuple<string, string>>()
    {
        Tuple.Create<string, string>("A", "B"),
        Tuple.Create<string, string>("B", "A"), // duplicate
        Tuple.Create<string, string>("C", "B"),
        Tuple.Create<string, string>("C", "B"), // duplicate
        Tuple.Create<string, string>("A", "D")              
    };

    public static void Main()
    {
        myList
            .Select(x => new[] { x.Item1, x.Item2 }.OrderBy(s => s).ToArray())
            .Select(x => Tuple.Create<string,string>(x[0], x[1]))
            .Distinct()
            .Dump();
    }
}

输出：

Dumping object(System.Linq.<DistinctIterator>d__81`1[Tuple`2[String,String]])
[
   {
   Item1  : A
   Item2  : B
   ToString(): (A, B)
   },
   {
   Item1  : B
   Item2  : C
   ToString(): (B, C)
   },
   {
   Item1  : A
   Item2  : D
   ToString(): (A, D)
   }
]

Answer 5

要保留原件，请使用group by 而不是Distinct，这样我们仍然可以访问组的第一个元素：

直播代码：https://dotnetfiddle.net/LYZItb

using System;
using System.Collections.Generic;

using System.Linq;

public class Program
{
    static List<Tuple<string, string>> myList = new List<Tuple<string, string>>()
    {
        Tuple.Create<string, string>("B", "A"),
        Tuple.Create<string, string>("A", "B"), // duplicate
        Tuple.Create<string, string>("C", "B"),
        Tuple.Create<string, string>("C", "B"), // duplicate
        Tuple.Create<string, string>("A", "D"),
        Tuple.Create<string, string>("E", "F"),
        Tuple.Create<string, string>("F", "E"), // duplicate        
    };

    public static void Main()
    {

        var result =
            from y in 
                from x in myList
                select new { Original = x, SortedPair = new[] { x.Item1, x.Item2 }.OrderBy(s => s).ToArray() }  
                group y by new { NormalizedTuple = Tuple.Create<string,string>(y.SortedPair[0], y.SortedPair[1]) } into grp
            select new { Pair = grp.Key.NormalizedTuple, Original = grp.First().Original };


        foreach(var item in result)
        {
            Console.WriteLine("Pair: {0} {1}", item.Original.Item1, item.Original.Item2);
        }
    }
}

输出：

Pair: B A
Pair: C B
Pair: A D
Pair: E F