从列表选择Linq中的多个字段

问题描述

在ASP.NET C＃我有一个结构：

In ASP.NET C# I have a struct:

public struct Data
{
    public int item1;
    public int item2;
    public int category_id;
    public string category_name;
}

和我的人的名单。我想选择 CATEGORY_ID 和 CATEGORY_NAME ，运行 DISTINCT 最后一个 ORDERBY 在 CATEGORY_NAME 。

and I have a List of those. I want to select category_id and category_name, running a DISTINCT and finally an ORDERBY on category_name.

这是我现在有：

List<Data> listObject = getData();
string[] catNames = listObject
                    .Select(i=> i.category_name)
                    .Distinct()
                    .OrderByDescending(s => s)
                    .ToArray();

这显然只是获取类别名称。我的问题是，我怎么得到多个领域，什么数据结构存储我在这（不是的String [] ）？

This obviously just gets the category name. My question is, how do I get multiple fields, and what data structure will I store this in (not a string[])?

修改

使用结构的名单不是一成不变的。如果这将是可取改变我的后盾的数据结构，使选择更简单（我会写很多这样的），那么我会乐意接受建议。

Using a list of structs is not set in stone. If it would be advisable to change my backing data structure to make selects easier (I'll be writing a lot of these) then I'd gladly take recommendations.

推荐答案

匿名类型允许您选择任意域到数据结构，有很强的在code类型以后：

Anonymous types allow you to select arbitrary fields into data structures that are strongly typed later on in your code:

var cats = listObject
    .Select(i => new { i.category_id, i.category_name })
    .Distinct()
    .OrderByDescending(i => i.category_name)
    .ToArray();

既然你（显然）需要将其存储供以后使用，您可以使用GROUPBY运算符：

Since you (apparently) need to store it for later use, you could use the GroupBy operator:

Data[] cats = listObject
    .GroupBy(i => new { i.category_id, i.category_name })
    .OrderByDescending(g => g.Key.category_name)
    .Select(g => g.First())
    .ToArray();

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