SortedSet. The C# SortedSet is an ordered set collection. It helps when we have many elements and want to store them in a sorted order, eliminating all duplicates.
This class is part of the System.Collections.Generic namespace. Its performance tends to be worse than a hash table like Dictionary—it does not support hashing.
First example. This program creates a new, empty SortedSet instance. Then it adds 3 elements to the set with the Add method. Finally it performs operations on the set.
Note The program invokes the Contains method to see if the string "bird" is present in the set.
Note 2 The program uses the SortedSet in "foreach" to loop through all the elements—they are stored alphabetically.
using System;
using System.Collections.Generic;
// Create sorted set.
SortedSet<string> set = new SortedSet<string>();
// Add 3 elements.
set.Add("carrot");
set.Add("bird");
set.Add("apple");
// Use contains method.
Console.WriteLine(set.Contains("bird"));
// Print all element in sorted order.
foreach (string val in set)
{
Console.WriteLine(val);
}True
apple
bird
carrot
Copy list. Often you may want to create a SortedSet instance from the elements in another collection, such as an array or List. You can do this with the SortedSet constructor.
Result In the example, the duplicate element ("perls") is only present once in the SortedSet.
using System;
using System.Collections.Generic;
// Create list with elements.
var list = new List<string>();
list.Add("x");
list.Add("y");
list.Add("perls");
list.Add("perls");
// Created sorted set from list.
SortedSet<string> set = new SortedSet<string>(list);
// Display contents.
foreach (string val in set)
{
Console.WriteLine(val);
}perls
x
y
RemoveWhere. Sometimes you may need to remove all elements from your SortedSet that match a certain condition. You can invoke the RemoveWhere method.
Here In this example, four names are added to the SortedSet that start with the letter s.
Then We call RemoveWhere with a lambda that is used as a predicate condition. When the method returns true, the element is removed.
using System;
using System.Collections.Generic;
// Create sorted set.
SortedSet<string> set = new SortedSet<string>();
set.Add("sam");
set.Add("sally");
set.Add("sandra");
set.Add("steve");
set.Add("mark");
set.Add("mark");
// Remove all elements where first letter is "s".
set.RemoveWhere(element => element.StartsWith("s"));
// Display.
foreach (string val in set)
{
Console.WriteLine(val);
}mark
Add method. We call the Add method to put additional elements into the set. The Add method returns a boolean value that tells us whether or not a new element was added.
Result If it returns true, a new element was added. If it returns false, the element already existed in the set and was not added again.
using System;
using System.Collections.Generic;
// Test add method.
SortedSet<string> set = new SortedSet<string>();
bool a = set.Add("sam");
bool b = set.Add("sam");
bool c = set.Add("sam");
bool d = set.Add("mike");
Console.WriteLine("{0} {1} {2} {3}", a, b, c, d);True False False True
Count, clear. As with other collections, you can use the Count property and the Clear method on the SortedSet type. The Count property can only be read, not assigned to.
using System;
using System.Collections.Generic;
SortedSet<string> set = new SortedSet<string>();
set.Add("a");
set.Add("z");
set.Add("a"); // Not successful.
Console.WriteLine(set.Count);
set.Clear();
Console.WriteLine(set.Count);2
0
UnionWith. This returns the union of two collections. If the set contains A, B and C, and the second collection contains C and D, the union will be equal to A, B, C and D.
Result The UnionWith method adds all the elements into one collection. No duplicates will be found in the SortedSet.
using System;
using System.Collections.Generic;
SortedSet<string> set = new SortedSet<string>();
set.Add("a");
set.Add("z");
set.Add("x");
List<string> list = new List<string>();
list.Add("a");
list.Add("y");
// Union the two collections.
set.UnionWith(list);
// Enumerate.
foreach (string val in set)
{
Console.WriteLine(val);
}a
x
y
z
SymmetricExceptWith. This returns all elements that are found in only one collection. If both contain "A," SymmetricExceptWith will remove "A" from the SortedSet instance.
Note The SymmetricExceptWith method modifies the SortedSet in-place. You do not need to copy the variable reference.
Important With SortedSet, some methods return a new SortedSet, and other modify the set in-place.
using System;
using System.Collections.Generic;
SortedSet<string> set = new SortedSet<string>();
set.Add("a");
set.Add("z");
set.Add("x");
List<string> list = new List<string>();
list.Add("a");
list.Add("y");
// Determine symmetric set.
set.SymmetricExceptWith(list);
// Display elements.
foreach (string val in set)
{
Console.WriteLine(val);
}x
y
z
ExceptWith. This removes all elements found in a collection from the SortedSet. The resulting SortedSet will contain all its elements except those that were found in the other collection.
using System;
using System.Collections.Generic;
SortedSet<string> set = new SortedSet<string>();
set.Add("a");
set.Add("z");
set.Add("x");
List<string> list = new List<string>();
list.Add("a");
list.Add("x");
// Call ExceptWith to remove elements.
set.ExceptWith(list);
// Display elements.
foreach (string val in set)
{
Console.WriteLine(val);
}z
Overlaps. This tells us whether a collection has any elements in common with the SortedSet. Even if only one element is found in common, the result is True. Otherwise the result is False.
using System;
using System.Collections.Generic;
SortedSet<string> set = new SortedSet<string>();
set.Add("a");
set.Add("z");
set.Add("x");
List<string> list = new List<string>();
list.Add("a");
list.Add("y");
HashSet<string> hash = new HashSet<string>();
hash.Add("v");
hash.Add("u");
bool a = set.Overlaps(list); // Set and list overlap.
bool b = set.Overlaps(hash); // Set and hash do not overlap.
Console.WriteLine(a);
Console.WriteLine(b);True
False
IntersectWith. This changes the set instance so that it contains only the elements that were present in both collections. The element count is reduced or stays the same.
using System;
using System.Collections.Generic;
var set = new SortedSet<string>();
set.Add("a");
set.Add("z");
set.Add("x");
var list = new List<string>();
list.Add("a");
list.Add("x");
// Compute intersection.
set.IntersectWith(list);
// Enumerate.
foreach (string val in set)
{
Console.WriteLine(val);
}a
x
Min, max. The SortedSet contains elements that are stored in ascending sorted order. So it is trivial for the set to compute its lowest and highest values.
Also You cannot use an indexer with the SortedSet, so these properties are useful.
using System;
using System.Collections.Generic;
// Three-element set.
var set = new SortedSet<string>();
set.Add("a");
set.Add("z");
set.Add("x");
// Write Min and Max.
Console.WriteLine(set.Min);
Console.WriteLine(set.Max);a
z
Subsets, supersets. SortedSet has methods to compute subsets and supersets. These are IsSubsetOf, IsSupersetOf, IsProperSubsetOf and IsProperSupersetOf.
Info A subset is contained entirely inside another set. A superset contains entirely another set.
Note Proper subsets and supersets cannot have the same number of elements. They must have at least one fewer.
using System;
using System.Collections.Generic;
var set = new SortedSet<string>();
set.Add("a");
set.Add("z");
set.Add("x");
var list1 = new List<string>();
list1.Add("a");
list1.Add("z");
list1.Add("x");
var list2 = new List<string>();
list2.Add("a");
list2.Add("z");
list2.Add("x");
list2.Add("y");
Console.WriteLine("IsProperSubsetOf: {0}", set.IsProperSubsetOf(list1));
Console.WriteLine("IsSubsetOf: {0}", set.IsSubsetOf(list1));
Console.WriteLine("IsProperSubsetOf: {0}", set.IsProperSubsetOf(list2));
Console.WriteLine("IsSubsetOf: {0}", set.IsSubsetOf(list2));
var list3 = new List<string>();
list3.Add("a");
list3.Add("z");
Console.WriteLine("IsProperSupersetOf: {0}", set.IsProperSupersetOf(list3));
Console.WriteLine("IsSupersetOf: {0}", set.IsSupersetOf(list3));IsProperSubsetOf: False
IsSubsetOf: True
IsProperSubsetOf: True
IsSubsetOf: True
IsProperSupersetOf: True
IsSupersetOf: True
SetEquals. This tells us if 2 collections have the same elements. In my testing, I found that the SetEquals method treats the second collection as though it has no duplicate elements.
Note If duplicate elements are present, the 2 collections may still be considered equal.
using System;
using System.Collections.Generic;
var set = new SortedSet<string>();
set.Add("s");
set.Add("a");
set.Add("m");
var list = new List<string>();
list.Add("s");
list.Add("a");
list.Add("m");
// See if the 2 collections contain the same elements.
bool a = set.SetEquals(list);
Console.WriteLine(a);True
GetViewBetween. How can you see what elements a SortedSet instance contains between and including 2 values? You can use GetViewBetween with 2 arguments: the minimum and maximum values.
using System;
using System.Collections.Generic;
var set = new SortedSet<int>();
set.Add(5);
set.Add(7);
set.Add(8);
set.Add(9);
set.Add(4);
// Call GetViewBetween method.
SortedSet<int> view = set.GetViewBetween(4, 7);
foreach (int val in view)
{
Console.WriteLine(val);
}4
5
7
Add. When you add elements to your SortedSet, they are automatically stored in ascending order: lowest to highest values. With Reverse() we get the elements in the opposite, reverse order.
And If you want to loop over your SortedSet from highest to lowest (reverse alphabetical order), you can call Reverse in a foreach-loop.
using System;
using System.Collections.Generic;
var set = new SortedSet<int>();
set.Add(8);
set.Add(7);
set.Add(8);
set.Add(9);
set.Add(3);
foreach (int val in set)
{
Console.Write(val);
Console.Write(' ');
}
Console.WriteLine();
// Use Reverse.
foreach (int val in set.Reverse())
{
Console.Write(val);
Console.Write(' ');
}
Console.WriteLine();3 7 8 9
9 8 7 3
Performance. Is SortedSet efficient? This depends of course on your program. A key point is that the SortedSet does not include hashing. To look up a node, a logarithmic search is needed.
Thus In micro-benchmarks, SortedSet is much slower than HashSet, but in real programs this difference may not be relevant.
Internally, the SortedSet is implemented as a tree with a Root, Left and Right node on every node instance. Every node is allocated on the managed heap. This reduces performance.
Detail For most programs a hashing mechanism (such as that found in Dictionary and HashSet) is superior for performance.
A summary. SortedSet can replace confusing, custom types with a simple type. This reduces program complexity. SortedSet is an interesting combination of HashSet and SortedList.
Dot Net Perls is a collection of tested code examples. Pages are continually updated to stay current, with code correctness a top priority.
Sam Allen is passionate about computer languages. In the past, his work has been recommended by Apple and Microsoft and he has studied computers at a selective university in the United States.
This page was last updated on Apr 26, 2023 (edit).
