LINQ投影元素計數

Question

假設：

var a = SomeCollection.OrderBy(...) 
       .Select(f => new MyType 
           { 
            counter = ? //I want counter value, so what first 
               //object have counter=1, second counter=2 
               //and so on 
            a=f.sometthing, 
            ... 
           }); 

如何設置這個計數器值？或者我是否會在事後迭代a？

Answer 1

使用Select的過載，它爲您提供當前元素的基於0的索引。

.Select((item, index) => new MyType 
      { 
       counter = index + 1, 
       a = item.Something 

Answer 2

只需捕獲變量：

int index = 1; 

var a = SomeCollection.OrderBy(...) 
     .Select(x => new MyType { counter = index++; }); 

計數器計數爲每個迭代被調用。