What is the best way to iterate over a Dictionary in C#?

Question

I've seen a few different ways to iterate over a Dictionary in C#. Is there a standard way?

Answer 1

It entirely depends on what you're looking for. There are collections for both the Keys and the Values so that you can iterate over either one depending your your needs.

Answer 2

  foreach(KeyValuePair<String,String> entry in MyDic)
  {
      // do something with entry.Value or entry.Key
  }

Answer 3

I would say foreach is the standard way, though it obviously depends on what you're looking for

foreach(var value in my_dictionary) {
  ...
}

Is that what you're looking for?

Answer 4

If you are trying to use a generic Dictionary in C# like you would use an associative array in another language:

foreach(KeyValuePair<string, string> item in myDictionary)
{
  foo(item.Key);
  bar(item.Value);
}

Or, if you only need to iterate over the collection of keys, use

foreach(var item in myDictionary.Keys)
{
  foo(item);
}

And lastly, if you're only interested in the values:

foreach(var item in myDictionary.Values)
{
  foo(item);
}

(Take note that the var keyword is an optional C# 3.0 feature, you could also use the exact type of your keys/values here)

Answer 5

There are plenty of options. My personal favorite is by KeyValuePair

Dictionary<string,object> myDictionary = new Dictionary<string,object>();
//Populate your dictionary here

Foreach (KeyValuePair<string,object> kvp in myDictionary)
{
     //Do some interesting things;
}

You can also use the Keys and Values Collections

Answer 6

Use the built in support for the iterator pattern, the foreach key word.

If using a non generic Dictionary, simply use the KeyValuePair type for the different items:

foreach(KeyValuePair item in myDictionary)
{
    DoStuffWith(item);
}

The generic version is almost identical, apart from defining the types in the KeyValuePair to be the same as the dictionary:

foreach(KeyValuePair<Tkey, Tvalue> item in myDictionary)
{
    DoStuffWith(item);
}

Answer 7

Depends on whether you're after the keys or the values...

From the MSDN Dictionary<(Of <(TKey, TValue>)>) Class description:

   // When you use foreach to enumerate dictionary elements,
    // the elements are retrieved as KeyValuePair objects.
    Console.WriteLine();
    foreach( KeyValuePair<string, string> kvp in openWith )
    {
        Console.WriteLine("Key = {0}, Value = {1}", 
            kvp.Key, kvp.Value);
    }

    // To get the values alone, use the Values property.
    Dictionary<string, string>.ValueCollection valueColl =
        openWith.Values;

    // The elements of the ValueCollection are strongly typed
    // with the type that was specified for dictionary values.
    Console.WriteLine();
    foreach( string s in valueColl )
    {
        Console.WriteLine("Value = {0}", s);
    }

    // To get the keys alone, use the Keys property.
    Dictionary<string, string>.KeyCollection keyColl =
        openWith.Keys;

    // The elements of the KeyCollection are strongly typed
    // with the type that was specified for dictionary keys.
    Console.WriteLine();
    foreach( string s in keyColl )
    {
        Console.WriteLine("Key = {0}", s);
    }

Answer 8

If say, you want to iterate over the values collection by default, I believe you can implement IEnumerable<>, Where T is the type of the values object in the dictionary, and "this" is a Dictionary.

public new IEnumerator<T> GetEnumerator()
{
   return this.Values.GetEnumerator();
}

Answer 9

I found this method in the documentation for the DictionaryBase class on MSDN:

foreach (DictionaryEntry de in myDictionary)
{
     //Do some stuff with de.Value or de.Key
}

This was the only one I was able to get functioning correctly in a class that inherited from the DictionaryBase.

Answer 10

You suggested below to iterate

Dictionary<string,object> myDictionary = new Dictionary<string,object>();
//Populate your dictionary here

foreach (KeyValuePair<string,object> kvp in myDictionary) {
    //Do some interesting things;
}

FYI, foreach doesn't work if the value are of type object.