C# - SortedList<TKey, TValue>
The SortedList<TKey, TValue>, and SortedList are collection classes that can store key-value pairs that are sorted by the keys based on the associated IComparer implementation.
For example, if the keys are of primitive types, then sorted in ascending order of keys.
C# supports generic and non-generic SortedList.
It is recommended to use generic SortedList<TKey, TValue> because it performs faster and less error-prone than the non-generic SortedList.
SortedList Characteristics
SortedList<TKey, TValue>is an array of key-value pairs sorted by keys.- Sorts elements as soon as they are added. Sorts primitive type keys in ascending order and object keys based on IComparer<T>.
- Comes under
System.Collection.Genericnamespace. - A key must be unique and cannot be null.
- A value can be null or duplicate.
- A value can be accessed by passing associated key in the indexer
mySortedList[key] - Contains elements of type KeyValuePair<TKey, TValue>
- It uses less memory than SortedDictionary<TKey,TValue>.
- It is faster in the retrieval of data once sorted, whereas
SortedDictionary<TKey, TValue>is faster in insertion and removing key-value pairs.
Creating a SortedList
The following example demonstrates how to create a generic SortedList<TKey, TValue>, and add key-value pairs in it.
//SortedList of int keys, string values
SortedList<int, string> numberNames = new SortedList<int, string>();
numberNames.Add(3, "Three");
numberNames.Add(1, "One");
numberNames.Add(2, "Two");
numberNames.Add(4, null);
numberNames.Add(10, "Ten");
numberNames.Add(5, "Five");
//The following will throw exceptions
//numberNames.Add("Three", 3); //Compile-time error: key must be int type
//numberNames.Add(1, "One"); //Run-time exception: duplicate key
//numberNames.Add(null, "Five");//Run-time exception: key cannot be null
In the above example, a generic SortedList<TKey, TValue> object is created by specifying the type of keys and values it is going to store.
The SortedList<int, string> will store keys of int type and values of string type.
The Add() method is used to add a single key-value pair in a SortedList.
Keys cannot be null or duplicate. If found, it will throw a run-time exception. Values can be duplicate and null if the type is nullable.
Use the collection-initializer syntax to initialize a SortedList with multiple key-value pairs at the time of instantiating, as shown below.
//Creating a SortedList of string keys, string values
//using collection-initializer syntax
SortedList<string,string> cities = new SortedList<string,string>()
{
{"London", "UK"},
{"New York", "USA"},
{ "Mumbai", "India"},
{"Johannesburg", "South Africa"}
};
The SortedList rearranges key-value pairs in the ascending order of keys as soon as a key-value pair added.
The following example displays all the keys and values using foreach loop.
SortedList<int,string> numberNames = new SortedList<int,string>()
{
{3, "Three"},
{5, "Five"},
{1, "One"}
};
Console.WriteLine("---Initial key-values--");
foreach(KeyValuePair<int, string> kvp in numberNames)
Console.WriteLine("key: {0}, value: {1}", kvp.Key , kvp.Value );
numberNames.Add(6, "Six");
numberNames.Add(2, "Two");
numberNames.Add(4, "Four");
Console.WriteLine("---After adding new key-values--");
foreach(var kvp in numberNames)
Console.WriteLine("key: {0}, value: {1}", kvp.Key , kvp.Value );
key: 1, value: One
key: 3, value: Three
key: 5, value: Five
---After adding new key-values--
key: 1, value: One
key: 2, value: Two
key: 3, value: Three
key: 4, value: Four
key: 5, value: Five
key: 6, value: Six
Accessing SortedList
Specify a key in the indexer sortedList[key], to get or set a value in the SortedList.
SortedList<int,string> numberNames = new SortedList<int,string>()
{
{3, "Three"},
{1, "One"},
{2, "Two"}
};
Console.WriteLine(numberNames[1]); //output: One
Console.WriteLine(numberNames[2]); //output: Two
Console.WriteLine(numberNames[3]); //output: Three
//Console.WriteLine(numberNames[10]); //run-time KeyNotFoundException
numberNames[2] = "TWO"; //updates value
numberNames[4] = "Four"; //adds a new key-value if a key does not exists
Above, numberNames[10] will throw a KeyNotFoundException because specified key 10 does not exist in a sortedlist.
To prevent this exception, use ContainsKey() or TryGetValue() methods, as shown below.
SortedList<int, string> numberNames = new SortedList<int,string>()
{
{3, "Three"},
{1, "One"},
{2, "Two"}
};
if(numberNames.ContainsKey(4)){
numberNames[4] = "four";
}
int result;
if(numberNames.TryGetValue(4, out result))
Console.WriteLine("Key: {0}, Value: {1}", 4, result);
Use Keys and Values properties if you want to iterate a SortedList using a for loop.
SortedList<int, string> numberNames = new SortedList<int,string>()
{
{3, "Three"},
{1, "One"},
{2, "Two"}
};
for (int i = 0; i < numberNames.Count; i++)
{
Console.WriteLine("key: {0}, value: {1}", numberNames.Keys[i], numberNames.Values[i]);
}
key: 2, value: Two
key: 3, value: Three
Remove Elements from SortedList
Use the Remove(key) and RemoveAt(index) methods to remove key-value pairs from a SortedList.
SortedList<int,string> numberNames = new SortedList<int,string>()
{
{3, "Three"},
{1, "One"},
{2, "Two"},
{5, "Five"},
{4, "Four"}
};
numberNames.Remove(1);//removes key 1 pair
numberNames.Remove(10);//removes key 1 pair, no error if not exists
numberNames.RemoveAt(0);//removes key-value pair from index 0
//numberNames.RemoveAt(10);//run-time exception: ArgumentOutOfRangeException
foreach(var kvp in numberNames)
Console.WriteLine("key: {0}, value: {1}", kvp.Key , kvp.Value );
key: 4, value: Four
key: 5, value: Five
SortedList Class Hierarchy
The following diagram illustrates the SortedList hierarchy.
Learn more about SortedList Methods and Properties on docs.microsoft.com