How do I get the list of keys in a Dictionary?

Question

I only want the Keys and not the Values of a Dictionary.

I haven't been able to get any code to do this yet. Using another array proved to be too much work as I use remove also.

How do I get a List of the Keys in a Dictionary?

Answer 1

Use the Dictionary<TKey,TValue>.Keys property:

List<string> keyList = new List<string>(this.yourDictionary.Keys);

Answer 2

You should be able to just look at .Keys:

    Dictionary<string, int> data = new Dictionary<string, int>();
    data.Add("abc", 123);
    data.Add("def", 456);
    foreach (string key in data.Keys)
    {
        Console.WriteLine(key);
    }

Answer 3

Update for .NET 3.5+

To get list of all keys:

using System.Linq;

List<String> myKeys = myDict.Keys.ToList();

If you face any issues using System.Linq, see the following:

• Visual Studio Does not recognize System.Linq
• System.Linq Namespace

Answer 4

Marc Gravell's answer should work for you. myDictionary.Keys returns an object that implements ICollection<TKey>, IEnumerable<TKey> and their non-generic counterparts.

I just wanted to add that if you plan on accessing the value as well, you could loop through the dictionary like this (modified example):

Dictionary<string, int> data = new Dictionary<string, int>();
data.Add("abc", 123);
data.Add("def", 456);

foreach (KeyValuePair<string, int> item in data)
{
    Console.WriteLine(item.Key + ": " + item.Value);
}

Answer 5

I can't believe all these convoluted answers. Assuming the key is of type: string (or use 'var' if you're a lazy developer): -

List<string> listOfKeys = theCollection.Keys.ToList();

Answer 6

The question is a little tricky to understand but I'm guessing that the problem is that you're trying to remove elements from the Dictionary while you iterate over the keys. I think in that case you have no choice but to use a second array.

ArrayList lList = new ArrayList(lDict.Keys);
foreach (object lKey in lList)
{
  if (<your condition here>)
  {
    lDict.Remove(lKey);
  }
}

If you can use generic lists and dictionaries instead of an ArrayList then I would, however the above should just work.

Answer 7

Or like this:

List< KeyValuePair< string, int > > theList =
    new List< KeyValuePair< string,int > >(this.yourDictionary);

for ( int i = 0; i < theList.Count; i++)
{ 
  // the key
  Console.WriteLine(theList[i].Key);
}

Answer 8

For a hybrid dictionary, I use this:

List<string> keys = new List<string>(dictionary.Count);
keys.AddRange(dictionary.Keys.Cast<string>());

Answer 9

I often used this to get the key and value inside a dictionary: (VB.Net)

 For Each kv As KeyValuePair(Of String, Integer) In layerList

 Next

(layerList is of type Dictionary(Of String, Integer))