How to use Aggregate method of Dictionary<> in C#?

Question

I'm a beginner in C#. I have a dictionary like this :

{
  {"tom", "student"},
  {"rob", "teacher"},
  {"david", "lawyer"}
}

I want to form this line :

tom = student, rob = teacher, david = lawyer

I want to use Aggregate extension method of dictionary<> but when i do it like this :

Console.WriteLine(dic.Aggregate((a,b) => (a.Key + " = " + a.Value + ", " + b.Key + " = " + b.Value)));

I get this error :

Cannot convert lambda expression to delegate type.

So it seems that i'm doing it wrong. So can anybody tell me how to use this method?

Answer 1

Aggregate is not a method from Dictionary, it's an extension method for IEnumerable<T>. If you want to build aggregated string:

dic.Aggregate(new StringBuilder(),
              (sb, kvp) => sb.AppendFormat("{0}{1} = {2}", 
                           sb.Length > 0 ? ", " : "", kvp.Key, kvp.Value),
              sb => sb.ToString());

Explanation:

• First parameter is accumulator, which will accumulate result
• Second parameter is a function, which will be invoked on each dictionary element. This function appends data to accumulator.
• Last parameter builds result string from accumulator

By the way you can use following code to build required string:

String.Join(", ", dic.Select(kvp => kvp.Key + " = " + kvp.Value));