Join and GroupJoin operations in C Sharp (C#) - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to join two lists on the Id property.

C Sharp (C#)

var result = from c in customers
             join o in orders on c.Id [1] o.CustomerId
             select new { c.Name, o.OrderId };

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

A==

Bequals

CequalsTo

Dequal

Attempts:

3 left

💡 Hint

Common Mistakes

Using '==' instead of 'equals' in join clause.

Using incorrect keywords like 'equal' or 'equalsTo'.

In C#, the join clause uses the keyword equals to match keys.

2fill in blank

medium

Complete the code to perform a GroupJoin and select the customer name with their orders.

C Sharp (C#)

var result = customers.GroupJoin(orders,
                c => c.Id,
                o => o.CustomerId,
                (c, os) => new { c.Name, Orders = [1] });

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

Ao

Borders

CorderList

Dos

Attempts:

3 left

💡 Hint

Common Mistakes

Using the original orders list instead of the grouped orders parameter.

Using a variable name not defined in the lambda parameters.

The GroupJoin result selector uses the second parameter (here named os) which represents the grouped orders for each customer.

3fill in blank

hard

Fix the error in the join clause by completing the missing keyword.

C Sharp (C#)

var query = from a in authors
            join b in books on a.Id [1] b.AuthorId
            select new { a.Name, b.Title };

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

Aequals

BequalsTo

CequalTo

D==

Attempts:

3 left

💡 Hint

Common Mistakes

Using '==' instead of 'equals'.

Using incorrect keywords like 'equalTo' or 'equalsTo'.

The join clause requires the keyword equals to compare keys, not '==' or other variants.

4fill in blank

hard

Fill both blanks to create a dictionary of customer names and their order counts using GroupJoin.

C Sharp (C#)

var customerOrderCounts = customers.GroupJoin(orders,
                            [1],
                            [2],
                            (c, os) => new { c.Name, Count = os.Count() })
                            .ToDictionary(x => x.Name, x => x.Count);

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

Ac => c.Id

Bo => o.CustomerId

Cc => c.Name

Do => o.Id

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up key selectors by using names instead of Ids.

Using order Id instead of CustomerId for matching.

The GroupJoin requires key selectors for customers and orders: customer Id and order CustomerId.

5fill in blank

hard

Fill all three blanks to join authors and books, then select author name, book title, and year published.

C Sharp (C#)

var joinedData = from a in authors
                 join b in books on a.Id [1] b.AuthorId
                 select new { [2], [3], b.YearPublished };

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

Aequals

Ba.Name

Cb.Title

D==

Attempts:

3 left

💡 Hint

Common Mistakes

Using '==' instead of 'equals' in join.

Selecting wrong properties or missing one.

The join uses equals. The select projects author name and book title along with year.