Why advanced LINQ matters in C Sharp (C#) - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to select all even numbers from the list using LINQ.

C Sharp (C#)

var evens = numbers.Where(n => n [1] 2 == 0).ToList();

Drag options to blanks, or click blank then click option'

A%

B/

C*

D+

Attempts:

3 left

💡 Hint

Common Mistakes

Using division operator instead of modulo.

Using multiplication or addition operators.

The modulo operator % returns the remainder. Using n % 2 == 0 checks if a number is even.

2fill in blank

medium

Complete the code to order the list of strings by their length using LINQ.

C Sharp (C#)

var ordered = words.OrderBy(w => w.[1]).ToList();

Drag options to blanks, or click blank then click option'

ACount

BLength

CSize

DLength()

Attempts:

3 left

💡 Hint

Common Mistakes

Using Length() as if it were a method.

Using Count which is for collections, not strings.

Strings have a property Length that gives their length. Use it without parentheses.

3fill in blank

hard

Fix the error in the LINQ query to select distinct names from the list.

C Sharp (C#)

var distinctNames = names.[1]().ToList();

Drag options to blanks, or click blank then click option'

AUnique

BUniqueNames

CDifferent

DDistinct

Attempts:

3 left

💡 Hint

Common Mistakes

Using non-existent methods like Unique or Different.

The correct LINQ method to get unique elements is Distinct().

4fill in blank

hard

Fill both blanks to create a dictionary with words as keys and their lengths as values, filtering words longer than 3 characters.

C Sharp (C#)

var dict = words.Where(w => w.[1] 3).ToDictionary(w => w, w => w.[2]);

Drag options to blanks, or click blank then click option'

A>

B<

CLength

DCount

Attempts:

3 left

💡 Hint

Common Mistakes

Using < instead of > for filtering.

Using Count instead of Length for strings.

We filter words longer than 3 using > 3 and use the Length property for values.

5fill in blank

hard

Fill all three blanks to create a dictionary with uppercase words as keys, their original words as values, filtering words starting with 'a'.

C Sharp (C#)

var dict = words.Where(w => w.[1]('a')).ToDictionary(w => w.[2](), w => w.[3]);

Drag options to blanks, or click blank then click option'

AStartsWith

BToUpper

CToString

DLength

Attempts:

3 left

💡 Hint

Common Mistakes

Using Length instead of ToString for values.

Using wrong methods for filtering or converting case.

We filter words starting with 'a' using StartsWith, convert keys to uppercase with ToUpper(), and use the original word as value with ToString().

Practice

1. What is the main benefit of using advanced LINQ in C# programming?

easy

A. It automatically fixes bugs in your code.

B. It makes the program run faster by using less memory.

C. It replaces the need for any loops in your program.

D. It simplifies complex data queries into readable code.

Solution

1. Step 1: Understand LINQ's purpose

   LINQ is designed to query and manipulate data collections easily.

2. Step 2: Identify the main benefit

   Advanced LINQ makes complex data queries simpler and more readable.

3. Final Answer:

   It simplifies complex data queries into readable code. -> Option D

4. Quick Check:

   Advanced LINQ = Simplifies queries [OK]

Hint: Think: LINQ turns complex data tasks into simple code [OK]

Common Mistakes:

• Confusing LINQ with performance optimization
• Believing LINQ fixes bugs automatically
• Thinking LINQ removes all loops

2. Which of the following is the correct syntax to filter a list of numbers using LINQ to select only even numbers?

easy

A. var evens = numbers.Select(n => n % 2 == 0);

B. var evens = numbers.Where(n => n % 2 == 0);

C. var evens = numbers.Filter(n => n % 2 == 0);

D. var evens = numbers.FindAll(n => n % 2 == 0);

Solution

1. Step 1: Identify LINQ filtering method

   The correct LINQ method to filter is Where.

2. Step 2: Check syntax correctness

   numbers.Where(n => n % 2 == 0) correctly filters even numbers.

3. Final Answer:

   var evens = numbers.Where(n => n % 2 == 0); -> Option B

4. Quick Check:

   Filter with Where = var evens = numbers.Where(n => n % 2 == 0); [OK]

Hint: Use Where for filtering in LINQ [OK]

Common Mistakes:

• Using Select instead of Where for filtering
• Using non-existent Filter method
• Confusing FindAll (List method) with LINQ

3. What will be the output of this code?

var numbers = new List<int> {1, 2, 3, 4, 5};
var result = numbers.Where(n => n > 3).Select(n => n * 2);
foreach(var num in result) Console.Write(num + " ");

medium

A. 6 8 10

B. 4 6 8 10

C. 8 10

D. 2 4 6 8 10

Solution

1. Step 1: Filter numbers greater than 3

   From the list {1,2,3,4,5}, numbers > 3 are 4 and 5.

2. Step 2: Multiply filtered numbers by 2

   4 * 2 = 8, 5 * 2 = 10.

3. Final Answer:

   8 10 -> Option C

4. Quick Check:

   Filter >3 then *2 = 8 10 [OK]

Hint: Filter first, then transform with Select [OK]

Common Mistakes:

• Multiplying before filtering
• Including numbers not > 3
• Confusing Select and Where order

4. Identify the error in this LINQ query:

var names = new List<string> {"Anna", "Bob", "Cathy"};
var result = names.Select(n => n.StartsWith("A"));
Console.WriteLine(string.Join(", ", result));

medium

A. The Select method should be Where to filter names starting with 'A'.

B. The StartsWith method is used incorrectly and causes a syntax error.

C. The string.Join method cannot join boolean values.

D. The list initialization syntax is wrong.

Solution

1. Step 1: Understand Select vs Where

   Select transforms each item; Where filters items based on condition.

2. Step 2: Identify correct method for filtering

   To get names starting with 'A', use Where, not Select.

3. Final Answer:

   The Select method should be Where to filter names starting with 'A'. -> Option A

4. Quick Check:

   Filter with Where, not Select [OK]

Hint: Use Where to filter, Select to transform [OK]

Common Mistakes:

• Using Select instead of Where for filtering
• Thinking StartsWith causes syntax error
• Believing string.Join can't join booleans

5. Given a list of products with properties Name and Price, how can you use advanced LINQ to create a dictionary where keys are product names and values are prices, but only include products priced above 100?

hard

A. products.Where(p => p.Price > 100).ToDictionary(p => p.Name, p => p.Price);

B. products.ToDictionary(p => p.Name, p => p.Price > 100);

C. products.Select(p => new {p.Name, p.Price > 100}).ToDictionary();

D. products.Where(p => p.Price > 100).Select(p => p.Name, p => p.Price);

Solution

1. Step 1: Filter products priced above 100

   Use Where(p => p.Price > 100) to select only those products.

2. Step 2: Convert filtered list to dictionary

   Use ToDictionary(p => p.Name, p => p.Price) to create dictionary with name keys and price values.

3. Final Answer:

   products.Where(p => p.Price > 100).ToDictionary(p => p.Name, p => p.Price); -> Option A

4. Quick Check:

   Filter then ToDictionary = products.Where(p => p.Price > 100).ToDictionary(p => p.Name, p => p.Price); [OK]

Hint: Filter first, then use ToDictionary with key and value selectors [OK]

Common Mistakes:

• Trying to use ToDictionary without filtering first
• Passing boolean expressions as dictionary values
• Incorrect use of Select for dictionary creation