c# - 将 LINQ 查询转换为字典

Question

我有一个返回以下格式的查询：

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

我想把它转换成这样的字典<string, string[]>：

{ "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，我没有任何运气。我认为这实际上是在尝试添加单个项目，例如"tesla" : ["model s"]，"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

You would need to group each item by the key first, then construct the dictionary:

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());

Of course, an ILookup<string, string> much easier:

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

Answer 2

You're looking for ToLookup if you would like the results to be grouped into a dictionary-like object:

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

Otherwise you will have to group the results first:

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

Answer 3

你要的是GroupBy()，其次ToDictionary()。

例子：

var result = query.GroupBy(q => q.Manufacturer).ToDictionary(q => q.Key, q => q.Value.ToArray());

什么GroupBy()是将具有相同匹配键选择器的所有元素分组。因此，当您告诉它时GroupBy(q => q.Manufacturer)，具有相同制造商的所有元素将组合在一起IEnumerable<T>。

Answer 4

使用ToLookup：

var table = pairs.ToLookup(kvp => kvp.Key, kvp => kvp.Value);

foreach(var i in table["tesla"])
   Console.WriteLine(i);