how to use hashtable in Linq

Question

I am trying to use hash table in linq to fetch the key whose value is ABC. What I have done so far:

Hashtable h=new Hashtable ();
h.Add(1 , "ABC");
h.Add(2 , "AgC");
h.Add(3 , "ABC");
h.Add(4 , "AhC");

Expected output: 1, 3 (keys having value "ABC")

ICollection c= h.Keys;

var posi= from a in c
          where h[a]="ABC"
          select a;

But the above query is not working and giving compile time error.

The error is:

could not find an implementation of the query pattern for source type 'System.Collections.ICollection'.

What I am doing wrong? I am new to C#. How to use Hashtable in LINQ?

Answer 1

You should not use non-generic HashTable to start with. Use generic Dictionary<int, string> instead:

var d = new Dictionary<int, string>();
d.Add(1 , "ABC");
d.Add(2 , "AgC");
d.Add(3 , "ABC");
d.Add(4 , "AhC");

var posi = from a in d
           where a.Value == "ABC"
           select a.Key;