如何获得linq groupby中分组值的列表？ [英] How to get a list of the grouped values in linq groupby?

问题描述

我有一个KeywordInstance类型的对象列表，它代表一个关键字，并且数据库的ID该关键字应用于的记录。

 关键字RecordID 
巨噬细胞1 
巨噬细胞2 
细胞周期3 
地图激酶2 
细胞周期1 
  

我想要的是所有关键字的集合，与每个关键字应用到的RecordID列表

 关键字RecordIDs 
巨噬细胞1，2 
细胞周期1，3 
 map激酶2 
  

我尝试使用Linq将它变成新对象。我只设法得到不同的关键字。

var keywords = allwords
.GroupBy（w => w.keyword）
.Select（g => new {keyword = g.Key }）;

问题是我似乎无法以任何方式获得g的值。 g是IGrouping类型，并且通过文档，它只具有属性Key，但不包括属性Value。我在互联网上看到的所有例子都只是告诉我选择g本身，但是结果是

  var keywords = allWords 
 .GroupBy（w => w.keyword）
 .Select（g => new {keyword = g.Key，RecordIDs = g}）; 
  

不是我想要的。

任何尝试从g中获取某些内容都会失败，并显示错误消息 System.Linq.IGropuing< string，UserQuery.KeywordInstance>没有[我尝试过的] 的定义。

我在这里做错了什么？

解决方案

我认为您已经接近您的解决方案。

  var keywords = allwords 
 .GroupBy（w => w.keyword）
 .Select（g => new 
 {
 keyword = g.Key，
 RecordIDs = g.Select（c => c.ID）
}）; 
  

只需选择您需要的记录。<
您看到 Keyword -column以及 ID -column的原因是因为它是 g的一部分

Linq newbie here, struggling with my first group by query.

I have a list of objects of type KeywordInstance which represent a keyword, and the ID of the database record to which the keyword was applied.

Keyword      RecordID
macrophages  1
macrophages  2
cell cycle   3 
map kinase   2
cell cycle   1

What I want to have is a collection of all keywords, with a list of the RecordIDs to which each keyword was applied

Keyword     RecordIDs 
macrophages 1, 2
cell cycle  1, 3
map kinase  2

I tried using Linq to get it into a new object. I only managed to get the distinct keywords.

var keywords = allWords .GroupBy(w => w.keyword) .Select(g => new {keyword = g.Key});

The problem is that I can't seem to get the values of g in any way. g is of the type IGrouping and by documentation, it only has the property Key, but not even the property Value. All the examples I have seen on the Internet for groupby just tell me to select g itself, but the result of

var keywords = allWords
    .GroupBy(w => w.keyword)
    .Select(g => new {keyword = g.Key, RecordIDs = g});

is not what I want.

Any try to get something out of g fails with the error message System.Linq.IGropuing<string, UserQuery.KeywordInstance> does not have a definition for [whatever I tried].

What am I doing wrong here?

解决方案

I think you are close to you solution.

var keywords = allWords
    .GroupBy(w => w.keyword)
    .Select(g => new 
           { 
              keyword = g.Key, 
              RecordIDs = g.Select(c => c.ID)
           });

Just Select the records you need.
The reason you are seeing the Keyword-column as well as the ID-column, is becuase it's part of g

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