LINQ Practice Tasks

Elementary 🔥

These tasks cover various LINQ methods like Sum(), Where(), OrderBy(), Count(), Max(), Distinct(), FirstOrDefault(), and Aggregate(), offering a practical way to enhance your LINQ skills.

Here's a table with a brief description of each LINQ method and links to their MSDN documentation:

Method	Description	MSDN Link
`Sum()`	Calculates the sum of a sequence of numeric values.	Sum
`Where()`	Filters a sequence based on a predicate.	Where
`OrderBy()`	Sorts the elements of a sequence in ascending order.	OrderBy
`Count()`	Counts the elements in a sequence, optionally with a predicate.	Count
`Max()`	Finds the maximum value in a sequence.	Max
`Distinct()`	Returns distinct elements from a sequence.	Distinct
`FirstOrDefault()`	Returns the first element of a sequence, or a default value if empty.	FirstOrDefault
`Aggregate()`	Applies an accumulator function over a sequence.	Aggregate

Task 1: Find the Sum

Description: Given an array of integers, find the sum of all elements.

int[] numbers = { 1, 2, 3, 4, 5 };
var sum = 0;
Console.WriteLine("Sum: " + sum);

Task 2: Get Even Numbers

Description: From an integer array, create a new array containing only even numbers.

int[] numbers = { 1, 2, 3, 4, 5 };
var evenNumbers = new[] {};
Console.WriteLine("Even Numbers: " + string.Join(", ", evenNumbers));

Task 3: Sort Strings Alphabetically

Description: Sort a string array in alphabetical order.

string[] strings = { "apple", "orange", "banana" };
var sortedStrings = strings;
Console.WriteLine("Sorted: " + string.Join(", ", sortedStrings));

Task 4: Count Specific Element

Description: Count how many times a specific number appears in an integer array.

int[] numbers = { 1, 2, 2, 3, 4, 2 };
var count = numbers;
Console.WriteLine("Count of 2: " + count);

Task 5: Filter by Length

Description: Find all strings in an array with a length greater than 3.

string[] strings = { "hi", "hello", "world", "yes", "no" };
var longStrings = strings;
Console.WriteLine("Strings longer than 3: " + string.Join(", ", longStrings));

Task 6: Find Maximum Value

Description: Find the maximum value in an integer array.

int[] numbers = { 1, 2, 3, 4, 5 };
var max = 0;
Console.WriteLine("Max: " + max);

Task 7: Concatenate Strings

Description: Concatenate all strings in an array into a single string. Do not use string.Join() as a solution. It allows to achieve the goal, but it's not a part of LINQ

string[] strings = { "apple", "orange", "banana" };
var concatenated = string.Join("", strings);
Console.WriteLine("Concatenated: " + concatenated);

Task 8: Distinct Elements

Description: Create a new array of distinct elements from an integer array.

int[] numbers = { 1, 2, 2, 3, 4, 2 };
var distinctNumbers = numbers;
Console.WriteLine("Distinct: " + string.Join(", ", distinctNumbers));

Task 9: First Element or Default

Description: Get the first element of an integer array, or a default value if empty.

int[] numbers = { 1, 2, 3, 4, 5 };
var firstOrDefault = 0;
Console.WriteLine("First or Default: " + firstOrDefault);

Task 10: Aggregate Strings

Description: Aggregate elements of a string array into a single string, separated by a comma.

string[] strings = { "apple", "orange", "banana" };
var aggregated = string.Join(", ", strings);
Console.WriteLine("Aggregated: " + aggregated);

Easy 🔥🔥

LINQ Method	Description	MSDN Link
Where	Filters a sequence of values based on a predicate	Where
Select	Projects each element of a sequence into a new form	Select
OrderBy	Sorts the elements of a sequence in ascending order	OrderBy
OrderByDescending	Sorts the elements of a sequence in descending order	OrderByDescending
GroupBy	Groups the elements of a sequence based on a key selector	GroupBy
Join	Joins two sequences based on matching keys	Join
Count	Returns the number of elements in a sequence	Count
Any	Determines whether any element of a sequence satisfies a condition	Any
Take	Returns a specified number of contiguous elements from the start of a sequence	Take
Distinct	Returns distinct elements from a sequence	Distinct

Task 1: Filter Even Numbers

Description: Filter a list of integers to select only even numbers.

List<int> numbers = new List<int> { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };
var evenNumbers = ___;
Console.WriteLine(string.Join(",", evenNumbers))

Task 2: Find Longest Word

Description: Find the longest word in a list of strings.

List<string> words = new List<string> { "apple", "banana", "orange", "grapefruit" };
var longestWord = ___;
Console.WriteLine("Longest word: " + longestWord);

Task 3: Calculate Average

Description: Calculate the average of a list of decimal numbers.

List<decimal> decimals = new List<decimal> { 2.5m, 3.7m, 1.9m, 4.2m };
var average = ___;
Console.WriteLine("Average: " + average);

Task 4: Group by Property

Description: Group a list of objects by a specific property.

public record Person(string name, int age, string country);

List<Person> people = new List<Person>
{
    new Person { Name = "Alice", Age = 25, Country = "USA" },
    new Person { Name = "Bob", Age = 30, Country = "UK" },
    new Person { Name = "Charlie", Age = 22, Country = "USA" },
    new Person { Name = "David", Age = 35, Country = "Canada" },
    new Person { Name = "Emily", Age = 28, Country = "UK" }
};

var grouped = ___;
foreach (var group in grouped)
{
    Console.WriteLine("Group: " + group.Key);
    foreach (var item in group)
    {
        Console.WriteLine(item);
    }
}

Task 5: Join Lists

Description: Join two lists based on a common property.

public record Person(string name, int age, string country);

List<Person> people1 = new List<Person>
{
    new Person { Name = "Alice", Country = "USA" },
    new Person { Name = "Bob", Country = "UK" },
    new Person { Name = "Charlie", Country = "USA" }
};

List<Person> people2 = new List<Person>
{
    new Person { Name = "David", Country = "Canada" },
    new Person { Name = "Emily", Country = "UK" }
};

var joined = ___;
foreach (var pair in joined)
{
    Console.WriteLine($"Item from list 1: {pair.Item1}, Item from list 2: {pair.Item2}");
}

Task 6: Sort Alphabetically

Description: Sort a list of strings alphabetically.

List<string> strings = new List<string> { "banana", "apple", "orange", "grape" };
var sorted = ___;
Console.WriteLine(string.Join(",", sorted))

Task 7: Select Distinct

Description: Select distinct elements from a list.

List<int> numbers = new List<int> { 1, 2, 2, 3, 3, 4, 4, 5, 5 };
var distinctNumbers = ___;
Console.WriteLine(string.Join(",", distinctNumbers))

Task 8: Retrieve Top 5 Highest Values

Description: Retrieve the top 5 highest values from a list of integers.

List<int> numbers = new List<int> { 10, 5, 8, 3, 12, 15, 6, 7, 9, 2 };
var top5 = ___;
Console.WriteLine(string.Join(",", top5))

Task 9: Check Condition

Description: Check if any element in a list satisfies a specific condition.

List<int> numbers = new List<int> { 1, 2, 3, 4, 5 };
var anyGreaterThan3 = ___;
Console.WriteLine("Any number greater than 3: " + anyGreaterThan3);

Task 10: Convert to Uppercase

Description: Convert a list of strings to uppercase.

List<string> words = new List<string> { "apple", "banana", "orange" };
var uppercasedWords = ___;
Console.WriteLine(string.Join(",", uppercasedWords`))

Medium 🔥🔥🔥

Task 1: Find Common Elements

Description: Given two lists of integers, find the common elements between them.

Task 2: Aggregate Nested Collections

Description: Given a list of orders, each containing a list of order items, calculate the total cost of each order.

Task 3: Find Top N Students

Description: Given a list of students with their scores, find the top N students based on their scores.

Task 4: Group and Count

Description: Given a list of transactions, group them by product name and count the number of transactions for each product.

Task 5: Calculate Running Total

Description: Given a list of numbers, calculate the running total (cumulative sum) of the numbers.

Task 6: Find Anagrams

Description: Given a list of strings, find all pairs of strings that are anagrams of each other.

Task 7: Combine and Filter

Description: Given two lists of objects, combine them into a single list, then filter out elements based on certain criteria.

Task 8: Manipulate Date and Time

Description: Given a list of dates, find the difference in days between each consecutive pair of dates.

Task 9: Partition Data

Description: Given a list of integers, partition the data into two groups: one containing even numbers and the other containing odd numbers.

Task 10: Handle Null Values

Description: Given a list of objects that may contain null values, filter out the null values and perform an operation on the non-null values.

Advanced 🔥🔥🔥🔥

Tasks to Create Your Own LINQ Implementation:

Understanding LINQ Operators: Familiarize yourself with the standard LINQ operators such as Where, Select, OrderBy, GroupBy, etc. Understand their behavior and the expected output.
Implementing Query Operators: Start by implementing basic query operators such as Where and Select. These operators should filter and transform data, respectively, similar to their LINQ counterparts.
Supporting Deferred Execution: Ensure that your LINQ implementation supports deferred execution, meaning that query operations are not executed until the result is needed.
Handling Iterators: Implement iterators to iterate over collections and apply query operators. This involves implementing custom iterator methods such as GetEnumerator, MoveNext, and Current.
Testing and Debugging: Test your LINQ implementation thoroughly with various data sets and edge cases. Debug any issues that arise and ensure that the results match the expected behavior of LINQ operators.
Optimizing Performance: Optimize your LINQ implementation for performance by minimizing unnecessary iterations and avoiding excessive memory allocations. Use techniques such as lazy evaluation and caching to improve performance.

Useful Resources for LINQ Concepts:

Microsoft Docs: The official documentation for LINQ provides comprehensive explanations of LINQ concepts and operators. LINQ (Language-Integrated Query)
LINQ Tutorial: Follow a LINQ tutorial to learn how LINQ works and how to use it effectively in C#. There are many tutorials available online that cover LINQ basics and advanced topics.
Books on LINQ: Consider reading books dedicated to LINQ programming, such as "LINQ Pocket Reference" by Joseph Albahari and Ben Albahari. These books provide in-depth coverage of LINQ concepts and techniques.

Useful Resources for Understanding Iterators and Deferred Execution:

Microsoft Docs - Iterators (C# Programming Guide): Learn about iterators in C# and how to use them to implement custom enumerable collections. Iterators (C# Programming Guide)
Microsoft Docs - Deferred Execution (LINQ to Objects): Understand deferred execution in LINQ and how it impacts query execution. Deferred Execution (LINQ to Objects)

Avoiding Tons of Enumerators:

Use yield return: When implementing custom iterators, use the yield return statement to return elements one at a time without creating multiple enumerables.
Reuse Iterators: Instead of creating new iterators for each LINQ operation, consider reusing existing iterators to minimize memory overhead.
Optimize Query Execution: Combine multiple LINQ operations into a single query to avoid unnecessary iterations and intermediate collections.
Use IEnumerable<T> and IEnumerator<T>: Implement custom collections and iterators using the IEnumerable<T> and IEnumerator<T> interfaces to ensure compatibility with LINQ operators and deferred execution.

By following these tasks and utilizing the recommended resources, you can create your own LINQ implementation and gain a deeper understanding of LINQ concepts and programming techniques in C#.

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