C# 使用C中的dictionary将某些自定义类属性用作同一类中另一个属性（形式为值）的唯一键

我有一个类类型say ValueSetting，如下所示，我正在尝试迭代List，以便对于列表中所有常见的param1、param2、param3条目，我必须对每个param4执行特定的操作。让我解释一下。在下表中，带有红色箭头标记param1、param2、param3的条目应该是类似于param4500600的list的键。因此，要巩固它们

10，foo，abc=>500600

20，boo，abc=>500600

30，foo，abc=>500

那么，这是我可以放在字典中的东西吗，用param1，param2，param3作为List的键？这是怎么做到的？还是有更好的方法来存储它们而不是字典

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可以使用您询问的方式来构造数据。从MSDN：

ToLookup方法返回一个查找，一个一对多的映射字典 值集合的键。查找不同于字典， 它执行键到单个值的一对一映射

要使用ToLookup方法创建查找，我们应定义：

具有重写的GetHashCode和Equals方法的键类；这个关键类将定义如何对输入数据进行分组； 用于从输入数据创建密钥的密钥选择器； 元素选择器，用于选择相应键的值。 第一种方法：使用匿名类型作为密钥

我们可以将其用作键来创建查找。匿名类型自动实现GetHashCode和Equals。从MSDN：

因为匿名类型上的Equals和GetHashCode方法是 根据的Equals和GetHashCode方法定义 属性，相同匿名类型的两个实例只有在 它们的所有性质都是相同的

以下是如何使用匿名类型作为密钥创建查找：

var list = new List<ValueSetting>
{
    new ValueSetting {param1 = 10, param2 = "foo", param3 = "abc", param4 = 500},
    new ValueSetting {param1 = 20, param2 = "boo", param3 = "abc", param4 = 500},
    new ValueSetting {param1 = 10, param2 = "foo", param3 = "abc", param4 = 600},
    new ValueSetting {param1 = 20, param2 = "boo", param3 = "abc", param4 = 600},
    new ValueSetting {param1 = 30, param2 = "foo", param3 = "abc", param4 = 500},
};

var lookup = list.ToLookup(
    vs => new {vs.param1, vs.param2, vs.param3}, // Group key.
    vs => vs.param4);                            // Group values.

foreach (var item in lookup)
{
    Console.WriteLine("{0} => ({1})", item.Key, string.Join(", ", item.Select(i => i)));
}

然后使用这个密钥类，我们可以创建一个查找：

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如果要从方法返回查找，或将其作为参数传递给另一个方法，或将其作为类的属性存储，以及在其他情况下创建查找时必须在创建查找的方法之外使用，则可以使用此方法。

似乎可以使用以下方法：

var list = new List<ValueSetting>
{
    new ValueSetting {param1 = 10, param2 = "foo", param3 = "abc", param4 = 500},
    new ValueSetting {param1 = 20, param2 = "boo", param3 = "abc", param4 = 500},
    new ValueSetting {param1 = 10, param2 = "foo", param3 = "abc", param4 = 600},
    new ValueSetting {param1 = 20, param2 = "boo", param3 = "abc", param4 = 600},
    new ValueSetting {param1 = 30, param2 = "foo", param3 = "abc", param4 = 500},
};

var grouped = list.GroupBy(x => new { x.param1, x.param2, x.param3 });

foreach (var grp in grouped)
{
    Console.WriteLine($"{grp.Key} => ({string.Join(", ", grp.Select(x => x.param4))})");
}

输出：

啊，托卢库普的用法很好。我认为这比在这里使用GroupBy要好。

public class Key
{
    public int param1;
    public string param2;
    public string param3;

    public override bool Equals(object obj)
    {
        if (ReferenceEquals(null, obj)) return false;
        if (ReferenceEquals(this, obj)) return true;
        if (obj.GetType() != GetType()) return false;
        Key other = (Key) obj;
        Key other = (Key) obj;
        return param1 == other.param1 && 
               string.Equals(param2, other.param2) && 
               string.Equals(param3, other.param3);
    }

    public override int GetHashCode()
    {
        unchecked
        {
            var hashCode = param1;
            hashCode = (hashCode * 397) ^ (param2 != null ? param2.GetHashCode() : 0);
            hashCode = (hashCode * 397) ^ (param3 != null ? param3.GetHashCode() : 0);
            return hashCode;
        }
    }
}

var list = new List<ValueSetting>
{
    new ValueSetting {param1 = 10, param2 = "foo", param3 = "abc", param4 = 500},
    new ValueSetting {param1 = 20, param2 = "boo", param3 = "abc", param4 = 500},
    new ValueSetting {param1 = 10, param2 = "foo", param3 = "abc", param4 = 600},
    new ValueSetting {param1 = 20, param2 = "boo", param3 = "abc", param4 = 600},
    new ValueSetting {param1 = 30, param2 = "foo", param3 = "abc", param4 = 500},
};

ILookup<Key, int> lookup = list.ToLookup(
    vs => new Key {param1 = vs.param1, param2 = vs.param2, param3 = vs.param3}, // Group key.
    vs => vs.param4); // Group values.

foreach (IGrouping<Key, int> item in lookup)
{
    Console.WriteLine("{0}, {1}, {2} => ({3})",
        item.Key.param1, item.Key.param2, item.Key.param3,
        string.Join(", ", item.Select(i => i)));
}

var list = new List<ValueSetting>
{
    new ValueSetting {param1 = 10, param2 = "foo", param3 = "abc", param4 = 500},
    new ValueSetting {param1 = 20, param2 = "boo", param3 = "abc", param4 = 500},
    new ValueSetting {param1 = 10, param2 = "foo", param3 = "abc", param4 = 600},
    new ValueSetting {param1 = 20, param2 = "boo", param3 = "abc", param4 = 600},
    new ValueSetting {param1 = 30, param2 = "foo", param3 = "abc", param4 = 500},
};

var grouped = list.GroupBy(x => new { x.param1, x.param2, x.param3 });

foreach (var grp in grouped)
{
    Console.WriteLine($"{grp.Key} => ({string.Join(", ", grp.Select(x => x.param4))})");
}

var grouped = list
    .GroupBy(x => new { x.param1, x.param2, x.param3 })
    .Select(grp => new { grp.Key, param4 = grp.Select(x => x.param4) });

foreach (var grp in grouped)
{
    Console.WriteLine($"{grp.Key} => ({string.Join(", ", grp.param4)})");
}

{ param1 = 10, param2 = foo, param3 = abc } => (500, 600)
{ param1 = 20, param2 = boo, param3 = abc } => (500, 600)
{ param1 = 30, param2 = foo, param3 = abc } => (500)