Get Dictionary key by using the dictionary value

Question

How to get the dictionary key by using the dictionary value?

when getting the value using the key its like this:

Dictionary<int, string> dic = new Dictionary<int, string>();  dic.Add(1, "a");  Console.WriteLine(dic[1]); Console.ReadLine(); 

How to do the opposite?

Answer 1

A dictionary is really intended for one way lookup from Key->Value.

You can do the opposite use LINQ:

var keysWithMatchingValues = dic.Where(p => p.Value == "a").Select(p => p.Key);  foreach(var key in keysWithMatchingValues)     Console.WriteLine(key); 

Realize that there may be multiple keys with the same value, so any proper search will return a collection of keys (which is why the foreach exists above).

Answer 2

Brute force.

        int key = dic.Where(kvp => kvp.Value == "a").Select(kvp => kvp.Key).FirstOrDefault();