Describing C# Collections. Definition, examples of use. Analogies

Collections 🔗

A collection is an object that contains a set of values and allows you to interact with these values (view, add, modify, delete, sort …) .

Classification of collections by characteristics 🔗

• Permanent, dynamic
• Can store objects of the same type or objects of different types

Classifying collections according to the logic of organization 🔗

• Vector - Array
• Matrix - Two-dimensional array
• Multidimensional array
• List - Ordered collection of objects
• Stack - last in - first out LIFO
• Queue - first in - first out FIFO
• Associative array (dictionary) - an unordered collection that stores key-value pairs
• Set - an unordered collection that stores a set of unique values
• A multiset is a set that allows the presence of several identical values at the same time.

Classify collections by implementation 🔗

Collection interfaces 🔗

IEnumerable<T>: defines the GetEnumerator method, you can get the elements of any collection The implementation of the interface allows you to iterate over the elements of the collection using foreach

ICollection<T>: represents common properties and methods for all generic collections (e.g. CopyTo, Add, Remove, Contains methods, Count property)

IList<T>: provides functionality for creating sequential lists

IComparer<T>: defines the Compare method for comparing two objects of the same type

IDictionary<TKey, TValue>: collection must store objects as key-value pairs TKey, TValue

IEqualityComparer<T>: defines methods by which two objects of the same type are compared for equality

are implemented by collection classes in the System.Collections.Generic namespace:

Required namespaces 🔗

using System.Collections;
using System.Collections.Generic;
using System.Collections.Specialized;

Collection types C# 🔗

• Array

ArrayList objectList = 
new ArrayList() 
{ 1, 2, "string", 'c', 2.0f };

• Singly linked list List<T>: sequential list. Implements interfaces IList<T>, ICollection<T>, IEnumerable<T>

List<int> numbers = 
new List<int>() { 1, 2, 3, 45 };

SortedSet<T>: a sorted collection of objects of the same type. Implements interfaces ICollection<T>, ISet<T>, IEnumerable<T>

SortedList<TKey, TValue>:stores sets of key-value pairs sorted by key. Implements interfaces ICollection<T>, IEnumerable<T>, IDictionary<TKey, TValue>

• Doubly linked list LinkedList<T>: Doubly linked list. Implements interfaces ICollection<T> , IEnumerable<T>

LinkedList<int> numbers1 = 
new LinkedList<int>();

• Stack Stack<T>: stack of similar objects. Implements interfaces ICollection<T> , IEnumerable<T>

Stack<int> numbers3 = 
new Stack<int>();

• Hash table Hashtable interfaces are implemented IDictionary, ICollection, IEnumerable, ISerializable, IDeserializationCallback и ICloneable

Hashtable htbl = new Hashtable();
htbl.Add("name", "key123");

• Bit array BitArray(byte[] bytes) And(),Get(),Not(),Or(),Set(),SetAll(),Xor()

BitVector32 CreateMask() CreateSelection()

BitArray bits1 = new BitArray(10);
var bits2 = new BitVector32 () ;

• Queue Queue<T>: FIFO(“first in, first out”). Implements interfaces ICollection, IEnumerable<T>

Queue<int> numbers2 = 
new Queue<int>();

• Dictionary Dictionary<TKey, TValue>: “key-value”. Implements interfaces ICollection<T>, IEnumerable<T>, IDictionary<TKey, TValue>

Dictionary<int, string> countries = 
new Dictionary<int, string>(5);

SortedDictionary<TKey, TValue>: stores sets of key-value pairs sorted by key. Similar to the SortedList<TKey, TValue> class, the main differences are only in memory usage and speed of insertion and deletion

• Ways to create collections

IEnumerable<int> randomCol =
Enumerable.Range(1, 10);

foreach (var item in randomCol)
 {
  Console.WriteLine((item.ToString());
 }
		
var r = new Random(Seed:5); 
var rVal = r.Next(minValue:1,maxValue:10);
		
IEnumerable<int> squares =
Enumerable.Range(20, 30).Select(x => x * rVal);		

Iterators and the yield statement 🔗

using System.Collections;
Numbers numbers = new Numbers();
foreach (int n in numbers)
{
Console.WriteLine(n);
}
class Numbers
{
	public IEnumerator GetEnumerator()
	{
	for(int i = 0; i < 6; i++)
	{
	yield return i * i;
	}
	}
}

• collections.workbook