转换字典＆LT; INT，可枚举＆GT;到词典＆LT; INT，可枚举＆GT;反相内容 [英] convert Dictionary<int, Enumerable> to Dictionary<int, Enumerable> inverting content

问题描述

为了清楚起见，可以说，我们有学生和类，它是一个多对多的关系。

我有一个字典，其中的关键是学生证和可枚举是类（比方说，我们只是有ID）的集合，我想要恢复这的classId的字典，学生

是有办法的LINQ做到这一点？我能想到的方法来与循环做到这一点，但我敢肯定是有办法做到这一点。

解决方案

  VAR newDic = DIC
   .SelectMany（双=＆GT; pair.Value
                           。选择（VAL =＆gt;新建{键= VAL，值= pair.Key}））
   .GroupBy（项目=＆GT; item.Key）
   .ToDictionary（GR =＆GT; gr.Key，GR =＆GT; gr.Select（项目=＆GT; item.Value））;
 

for clarity lets say we have students and classes, its a many to many relationship.

I have a Dictionary where the key is the student id and the Enumerable is a collection of classes(say we just have the id ) and I want to revert this to a Dictionary of classId, students

is there a way to do this with Linq? I can think of a way to do this with loops but I m sure there is a way to do this.

解决方案

var newDic = dic
   .SelectMany(pair => pair.Value
                           .Select(val => new { Key = val, Value = pair.Key }))
   .GroupBy(item => item.Key)
   .ToDictionary(gr => gr.Key, gr => gr.Select(item => item.Value));

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