In C# how do I get a list of the keys from a dictionary?

Question

I have the following code:

Dictionary <string, decimal> inventory; // this is passed in as a parameter. It is a map of name to price // I want to get a list of the keys. // I THOUGHT I could just do: List<string> inventoryList = inventory.Keys.ToList();

But I get the following error:

'System.Collections.Generic.Dictionary.KeyCollection' does not contain a definition for 'ToList' and no extension method 'ToList' accepting a first argument of type 'System.Collections.Generic.Dictionary.KeyCollection' could be found (are you missing a using directive or an assembly reference?)

Am I missing a using directive? Is there something other than

using System.Collections.Generic;

that I need?

EDIT

List < string> inventoryList = new List<string>(inventory.Keys);

works, but just got a comment regarding LINQ

yes, you also need using System.Linq;, because that's where the .ToList() extension method is defined — Cristian Lupascu
– Cristian Lupascu, Commented Aug 11, 2013 at 16:12
Don't include System.Linq; if you only need ToList() for this once instance, just call new List<string>(inventory.Keys) — Alan
– Alan, Commented Aug 11, 2013 at 16:16
And remember, an extension method can even be called like: Enumerable.ToList(inventory.Keys), because ToList<T>() is List<TSource> ToList<TSource>(this IEnumerable<TSource> source), where the this IEnumerable<TSource> source can even be passed explicitly (useful in the debugger, when you don't have the using System.Linq definde) — xanatos
– xanatos, Commented Aug 11, 2013 at 16:17
@xanatos - Enumerable class is in System.Linq so namespace needs to be added anyways. — Rohit Vats
– Rohit Vats, Commented Aug 11, 2013 at 16:20
@RohitVats But at least the Visual Studio will suggest it :-)... You are right, the exact command is System.Linq.Enumerable.ToList(inventory.Keys) — xanatos
– xanatos, Commented Aug 11, 2013 at 16:23

Sam Harwell · Accepted Answer · 2013-08-11 16:16:15Z

You can either use the Enumerable.ToList extension method, in which case you need to add the following:

using System.Linq;

Or you can use a different constructor of List<T>, in which case you don't need a new using statement and can do this:

List<string> inventoryList = new List<string>(inventory.Keys);

Thanks - I used the new/different ctor - I did not need to and linq just for this. I have to go back and see why i did not notice that in the docs - regarding linq inclusion

Rohit Vats · Accepted Answer · 2013-08-11 16:14:27Z

2

using System.Linq is missing which contains ToList() extension method.

answered Aug 11, 2013 at 16:14

Rohit Vats

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Comments

Rod Stephens · Accepted Answer · 2013-08-11 16:34:03Z

I think you should be able to loop through the Keys collection as in:

foreach (string key in inventory.Keys) { Console.WriteLine(key + ": " + inventory[key].ToString()); }

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