c# - 将 LINQ 查询转换为 Dictionary

Question

我有一个返回以下格式内容的查询:

{ "tesla", "model s" }
{ "tesla", "roadster" }
{ "honda", "civic" }
{ "honda", "accord" }

我想将其转换为 <string, string[]> 的字典像这样:

{ "tesla" : ["model s", "roadster"],  "honda" : ["civic", "accord"] }

我试过这个:

var result = query.Select(q => new { q.Manufacturer, q.Car}).Distinct().ToDictionary(q => q.Manufacturer.ToString(), q => q.Car.ToArray()); 

但到目前为止我运气不好。我认为这实际上是在尝试添加单个项目，例如 "tesla" : ["model s"]和 "tesla" : ["roadster"]这就是它失败的原因……有什么简单的方法可以完成我在 LINQ 中尝试做的事情吗？

Answer 1

您需要先按键对每个项目进行分组，然后构建字典:

result = query.Select(q => new { q.Manufacturer, q.Car}).Distinct()
              .GroupBy(q => q.Manufacturer)
              .ToDictionary(g => g.Key, 
                            g => g.Select(q => q.Car).ToArray());

当然，一个 ILookup<string, string> 容易得多:

result = query.Select(q => new { q.Manufacturer, q.Car }).Distinct()
              .ToLookup(q => q.Manufacturer, q => q.Car);