反向多到很多词典和LT;键，列表与LT;价值>> [英] Reverse many-to-many Dictionary<key, List<value>>

问题描述

前面的问题让我想起了
和我意识到，扭转了词典是不平凡的。
什么是最优雅，最可读的方式做到这一点？

Actually my previous question got me thinking and I realized that reversing a Dictionary is not trivial. What is the most elegant and readable way to do it?

同样的情景学生多对多带类

Same scenario student Many to Many with Classes

原 Dicitonary< INT，列表与LT; INT>> ，其中最关键的是studentId和值是列表< INT> 包含的classId，想要恢复到词典<的classId，列表与LT; studentId>>

original Dicitonary<int, List<int>> where the key is studentId and the Value is a List<int> that contains classId and want to revert to Dictionary<classId, List<studentId>>

感谢

更新：
其实我只是测试卢克和布鲁诺的解决方案，他们返回归类谁，他们都具有相同的学生适量，将更新为我走。

Update: Actually I just tested Luke and Bruno's solutions and they return the right amount of classed whoever they all have the same student, will update as i go along.

推荐答案

稍微不同的方式（更理解我的大脑有点反正:) ...

Slightly different way (a bit more comprehensible to my brain anyway :) ...

var newDict = new Dictionary<int, List<int>>();
var dict = new Dictionary<int, List<int>>();
dict.Add( 1, new List<int>() { 1, 2, 3, 4, 5 } );
dict.Add( 2, new List<int>() { 1, 2, 3, 4, 5 } );
dict.Add( 3, new List<int>() { 1, 2, 6 } );
dict.Add( 4, new List<int>() { 1, 6, 7 } );
dict.Add( 5, new List<int>() { 8 } );

var newKeys = dict.Values.SelectMany( v => v ).Distinct();

foreach( var nk in newKeys )
{
   var vals = dict.Keys.Where( k => dict[k].Contains(nk) );
   newDict.Add( nk, vals.ToList() );
}

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