从元组列表中删除重复项

Question

我有一个Tuple<string,string>对象的列表，我想删除重复项，例如，元组(a,b)和(b,a)被认为是相同的（这些是图形的边缘）。有什么好方法可以做到这一点？

Answer 1

您需要创建一个比较器，该比较器可以以这样的方式比较元组，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.Item2, y.Item1);
    }
    public int GetHashCode(Tuple<T, T> obj)
    {
        return comparer.GetHashCode(obj.Item1) ^ comparer.GetHashCode(obj.Item2);
    }
}

请注意，独占或哈希代码是一种操作，无论操作数的顺序如何，它都会产生相同的结果，因此在这里是可取的（但在大多数哈希代码生成算法中不是，因为它通常是一个不需要的属性）。 至于Equals，只需要检查两种可能的配对。

一旦你有了它，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，可以使用如下所示的 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。 您是否有一个不会出现在字符串中的字符，可以用作分隔符？ 在这个例子中，我选择了"："：

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

要保留原始元素，请使用 group by 而不是 Distinct ，以便我们仍然可以访问组的第一个元素：

实时代码：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

Answer 5

实时代码：https://dotnetfiddle.net/LUErFj

首先对元组对进行排序，然后执行 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)
   }
]