C# | Get a collection of keys in the StringDictionary

StringDictionary.Keys property is used to get a collection of keys in the StringDictionary.

Syntax:

public virtual System.Collections.ICollection Keys { get; }

Return Value: An ICollection that provides the keys in the StringDictionary.

Below given are some examples to understand the implementation in a better way:

Example 1:

// C# code to get a collection
// of keys in the StringDictionary
using System;
using System.Collections;
using System.Collections.Specialized;

class GFG {

    // Driver code
    public static void Main()
    {

        // Creating a StringDictionary named myDict
        StringDictionary myDict = new StringDictionary();

        // Adding key and value into the StringDictionary
        myDict.Add("A", "Apple");
        myDict.Add("B", "Banana");
        myDict.Add("C", "Cat");
        myDict.Add("D", "Dog");

        // To copy the StringDictionary values to
        // a one-dimensional Array instance at
        // the specified index.
        String[] myKeys = new String[myDict.Count];
        myDict.Keys.CopyTo(myKeys, 0);

        // Getting a collection of keys
        // in the StringDictionary
        for (int i = 0; i < myDict.Count; i++) {
            Console.WriteLine(myKeys[i] + " " + myDict[myKeys[i]]);
        }
    }
}

Output:

d Dog
b Banana
c Cat
a Apple

Example 2:

// C# code to get a collection
// of keys in the StringDictionary
using System;
using System.Collections;
using System.Collections.Specialized;

class GFG {

    // Driver code
    public static void Main()
    {

        // Creating a StringDictionary named myDict
        StringDictionary myDict = new StringDictionary();

        // Adding key and value into the StringDictionary
        myDict.Add("3", "prime & odd");
        myDict.Add("2", "prime & even");
        myDict.Add("4", "non-prime & even");
        myDict.Add("9", "non-prime & odd");

        // To copy the StringDictionary values to
        // a one-dimensional Array instance at
        // the specified index.
        String[] myKeys = new String[myDict.Count];
        myDict.Keys.CopyTo(myKeys, 0);

        // Getting a collection of keys
        // in the StringDictionary
        for (int i = 0; i < myDict.Count; i++) {
            Console.WriteLine(myKeys[i] + " " + myDict[myKeys[i]]);
        }
    }
}

Output:

2 prime & even
3 prime & odd
9 non-prime & odd
4 non-prime & even

Note:

• The order of the keys in the ICollection is unspecified, but it is the same order as the associated values in the ICollection returned by the Values method.
• The returned ICollection is not a static copy. Instead, the ICollection refers back to the keys in the original StringDictionary. Therefore, changes to the StringDictionary continue to be reflected in the ICollection.
• Retrieving the value of this property is an O(1) operation.

Reference:

• https://docs.microsoft.com/en-us/dotnet/api/system.collections.specialized.stringdictionary.keys?view=netframework-4.7.2