Top interview questions and answers related to C# Collection, Generic, LINQ, and Lambda expression

What is a collection in C#?

A collection is a group of objects of the same type that are stored together in memory.

What are generics in C#?

Generics are a feature of C# that allows developers to create classes, interfaces, and methods that can work with any type of data.

What is LINQ in C#?

LINQ stands for Language-Integrated Query and is a feature in C# that allows developers to write SQL-like queries directly in their code to query collections, databases, and other data sources.

What are lambda expressions in C#?

Lambda expressions are anonymous functions that can be used to create delegates or expression tree types in C#. They provide a concise way to write functions that can be passed as arguments to other methods.

How do you create a new List<T> in C#?

To create a new List<T> in C#, you can use the following code:

List<T> myList = new List<T>();

What is the difference between IEnumerable and IQueryable in C#?

IEnumerable is a read-only interface that allows developers to iterate over a collection of objects, whereas IQueryable allows developers to perform complex queries on a data source, such as a database.

How do you use LINQ to query a List<T> in C#?

To use LINQ to query a List<T> in C#, you can use the following code:

var query = from item in myList

            where item.Property == someValue

            select item;

How do you use a lambda expression in a LINQ query in C#?

To use a lambda expression in a LINQ query in C#, you can use the following code:

var query = myList.Where(item => item.Property == someValue);

What is the purpose of the GroupBy method in LINQ in C#?

The GroupBy method in LINQ allows developers to group objects in a collection based on a common property or key. It returns a collection of groups, where each group contains objects that have the same key.

How do you use the Select method in LINQ in C#?

To use the Select method in LINQ in C#, you can use the following code:

var query = myList.Select(item => item.Property);

What is a dictionary in C#?

A dictionary is a collection that stores key-value pairs. Keys are used to uniquely identify each value in the dictionary.

How do you add an item to a dictionary in C#?

To add an item to a dictionary in C#, you can use the following code:

myDictionary.Add(key, value);

What is the purpose of the ToList method in LINQ in C#?

The ToList method in LINQ is used to create a new list from the results of a query. It is often used to convert an IEnumerable to a List.

How do you sort a list in C#?

To sort a list in C#, you can use the following code:

myList.Sort();

This code will sort the list in ascending order. To sort the list in descending order, you can use the following code:

myList.Sort((x, y) => y.CompareTo(x));

What is the purpose of the FirstOrDefault method in LINQ in C#?

The FirstOrDefault method in LINQ is used to return the first element in a collection that satisfies a given condition. If no element satisfies the condition, it returns the default value for the element type.

How do you use the Any method in LINQ in C#?

The Any method in LINQ is used to determine whether a collection contains any elements that satisfy a given condition. To use the Any method in C#, you can use the following code:

bool result = myList.Any(item => item.Property == someValue);

What is the purpose of the Where method in LINQ in C#?

The Where method in LINQ is used to filter a collection based on a given condition. It returns a new collection that contains only the elements that satisfy the condition.

How do you use the Take method in LINQ in C#?

The Take method in LINQ is used to return a specified number of elements from the beginning of a collection. To use the Take method in C#, you can use the following code:

var query = myList.Take(5);

What is the purpose of the Distinct method in LINQ in C#?

The Distinct method in LINQ is used to remove duplicates from a collection. It returns a new collection that contains only the distinct elements of the original collection.

How do you use the SelectMany method in LINQ in C#?

The SelectMany method in LINQ is used to flatten a collection of collections into a single collection. To use the SelectMany method in C#, you can use the following code:

var query = myList.SelectMany(item => item.SubItems);

This code will create a new collection that contains all the sub-items of each item in the myList collection.

Can you explain the difference between a list and an array in C#?

Arrays have a fixed size and can't be resized once they are created, whereas lists can be resized dynamically. Lists are implemented using arrays but they provide additional methods for adding and removing elements, as well as other useful features like sorting and filtering.

How do you remove an item from a list in C#?

To remove an item from a list in C#, you can use the following code:

myList.Remove(item);

This code will remove the specified item from the list.Can you explain the difference between

  

IEnumerable and ICollection in C#?

IEnumerable is an interface that provides read-only access to a collection of objects, whereas ICollection is an interface that provides both read and write access to a collection of objects. ICollection inherits from IEnumerable and adds additional methods for adding, removing, and modifying elements.

How do you convert an array to a list in C#?

To convert an array to a list in C#, you can use the following code:

List<T> myList = myArray.ToList();

This code will create a new list from the elements of the array.

How do you use the Contains method in LINQ in C#? 

The Contains method in LINQ is used to determine whether a collection contains a specified element. To use the Contains method in C#, you can use the following code:

bool result = myList.Contains(item);

This code will return true if the list contains the specified item.

Can you explain the difference between IQueryable and IEnumerable in C#? 

IQueryable is an interface that provides the ability to perform queries against a data source that can be translated into a query language like SQL, whereas IEnumerable provides only read-only access to a collection of objects. IQueryable inherits from IEnumerable and adds additional methods for querying a data source.

How do you use the Distinct method with a custom comparer in LINQ in C#? 

To use the Distinct method with a custom comparer in LINQ in C#, you can use the following code:

var query = myList.Distinct(new MyEqualityComparer());

This code will create a new collection that contains only the distinct elements of the original collection, using the specified custom comparer to compare elements for equality.

How do you use the Any method with a predicate in LINQ in C#? 

To use the Any method with a predicate in LINQ in C#, you can use the following code:

bool result = myList.Any(item => item.Property == someValue);

This code will return true if any element in the collection satisfies the given predicate.

Can you explain the difference between a HashSet and a List in C#? 

A HashSet is a collection that stores unique elements, whereas a List can contain duplicate elements. HashSet provides fast lookup and insertion times but doesn't maintain the order of elements, whereas List maintains the order of elements but has slower lookup and insertion times.

How do you use the ToDictionary method in LINQ in C#? 

The ToDictionary method in LINQ is used to create a new dictionary from a collection, using a specified key selector and value selector. To use the ToDictionary method in C#, you can use the following code:

var dictionary = myList.ToDictionary(item => item.Key, item => item.Value);

This code will create a new dictionary from the myList collection, using the Key property as the key and the Value property as the value for each element in the collection.