用Linq覆盖/加入两个集合 [英] Overlay/Join two collections with Linq

问题描述

我有以下情况：

列表1有20个类型的项目，列表2有5个相同类型的项目。列表1已经包含来自列表2的项目，但处于不同的状态。我想用列表2中的项目覆盖列表1中的5个项目。

List 1 has 20 items of type TItem, List 2 has 5 items of the same type. List 1 already contains the items from List 2 but in a different state. I want to overwrite the 5 items in List 1 with the items from List 2.

我认为连接可能会工作，但是我想覆盖列表1中的项目，

I thought a join might work, but I want to overwrite the items in List 1, not join them together and have duplicates.

有一个唯一的键，可用于在List 1中找到要覆盖的项目，键类型为int

There is a unique key that can be used to find which items to overwrite in List 1 the key is of type int

推荐答案

您可以使用内置的Linq .Except（），但它想要一个IEqualityComparer，所以使用 .Except（）的流畅版本。

You could use the built in Linq .Except() but it wants an IEqualityComparer so use a fluid version of .Except() instead.

假设一个对象带有整数键，如下所示：

Assuming an object with an integer key as you indicated:

public class Item
{
    public int Key { get; set; }
    public int Value { get; set; }
    public override string ToString()
    {
        return String.Format("{{{0}:{1}}}", Key, Value);
    }
}

对象的原始列表可以与已更改的一个如下：

The original list of objects can be merged with the changed one as follows:

IEnumerable<Item> original = new[] { 1, 2, 3, 4, 5 }.Select(x => new Item
    {
        Key = x,
        Value = x
    });
IEnumerable<Item> changed = new[] { 2, 3, 5 }.Select(x => new Item
    {
        Key = x,
        Value = x * x
    });

IEnumerable<Item> result = original.Except(changed, x => x.Key).Concat(changed);
result.ForEach(Console.WriteLine);

输出：

{1:1}
{4:4}
{2:4}
{3:9}
{5:25}

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