C# Collections

Question 1

What is a collection?

Answer 1

a type whose purpose is to manage a group of objects in memory and to provide access to those objects.

Question 2

Microsoft collections types

Answer 2

Collections can be categorized as:

List - Dictionaries - Sets

Question 3

Lists

Answer 3

Order is important is a list. When need to look up position in a list.
index based
Array T[] and List are both index based list.
other index based list:
Collection
ReadOnlyCollection
ObservableCollection

Index based list are good for memory use and they are also efficient for accessing elements.

Question 4

Dictionaries

Answer 4

Not interested in index, but access items using its name. When you want to access some element in the collections you identified it using some piece of information that is unique to that element.
Dictionary
Dictionary are meant to be search using a key.

Question 5

Sets

Answer 5

The focus is on treating the collection as a single group and performing operation on the collection as a whole.
The set can allow you to find the intersect (common) in two sets or the union of two sets.
the most common set collection is: HashSet

Question 6

What type of operations a collection needs to support?

Answer 6

Two Types:
- Reading
Look up element
enumerating - ask for all items in collection

collections that do not allow you to look up items: Sets, Linked Lists, Stacks, Queues - Writing Add an element Remove an element Lists: Insert an element (replace an element)

Question 7

Array?

Answer 7

The most basic type of collection in .NET
an array is an index-based list.
array offer an very rich API, very lightweight and offer best performance for looking up elements, special c# syntax, they are fixed sized.

array is index based, first element is at index 0 and final element is at index (# of element) - 1.

arrays are reference typed. each element store their address which refer to the object

Question 8

IEnumerable

Answer 8

the most important interface. It purpose is that it declare that you can iterate my element. If something implements IEnumerable, then you can use LINK
Enumerable don’t necessary know how many items there are. IT’s read onlyon it.

Question 9

ICollection

Answer 9

“I know how many elements I have”
Identifies something as a collection.
Collection are expected to know how many items they contains.
It tells you that it’s a collection, but it doesn’t tell you what kind of collection it is.
IList, IDIctionary, ISet implements ICollection

Question 10

IEnumerator GetEnumerator

Answer 10

Enumerating a collection is done by a separate object named enumerator. The sole purpose of IEnumerator is to supply the enumerator.
Returns an enumerator
- the thing that does the enumerating

Question 11

IList

Answer 11

“You can access my elements with an index”
Array implements IList
Ability to enumerate element (index, indexOf)
Ability to modify the collection (Insert(), RemoveAt())

Question 12

IDictionary

Answer 12

like a list, but with keys instead of an index

it’s a collection of key value pair

Question 13

ISet

Answer 13

“Can do set operation with other collections”
Set operation, set comparison, Modify the collection
less widely used

Question 14

List

Answer 14

It’s a like an array. It gives a high performance and an index-based + adding and removing elements.

Question 15

Collection

Answer 15

Provides an implementation of IList

Collection is customizable

Question 16

IObservable

Answer 16

design to be a list to provide notification if the collection has changed

Question 17

LinkedList

Answer 17

purpose: Collection that is quick at adding and removing elements

Pros: Good at adding/removing elements, enumerating,
CON: No index-based access, use lots of memory

Question 18

Stack

Answer 18

The element place you can add or remove an element is at the last place.

Stack are referred to as last-in-first-out collection.

add - push is used to add element to the stack

remove - pop is used to remove element to the stack example: a stack book

Question 19

Queue

Answer 19

you can only add/remove the first element.

Queue are referred to as first-in-first-out collection.

enqueue - to add element
dequeue - to remove element
example: schedule, task are done in order.

Question 20

Dictionary

Answer 20

A Dictionary class is a data structure that represents a collection of keys and values pair of data. The key is identical in a key-value pair and it can have at most one value in the dictionary, but a value can be associated with many different keys.

Question 21

HashSet

Answer 21

has no sense of order. An element is in the collection or isn’t. Elements do not have index. There is no way to look an element.
HashSet guarantees uniqueness: never have the same element more than once.

Question 22

IEnumerable

IEnumerator

Answer 22

IEnumerable
Exposes the enumerator, which supports a simple iteration over a collection of a specified type.

IEnumerator
it’s like a cursor. has a method call MoveNext(), and a property call current.
bool MoveNext() – return true if there is a next item.
the enumerator will stop when there is no more item.
IEnumerator implement IDisposable.