9. Groups

Question 1

What does the LINQ GroupBy method do?

Answer 1

Groups the elements of a sequence.

Question 2

How do you group by elements in a LINQ query expression?

Answer 2

By using the group and the by keywords.

eg. group x by x.Field

Question 3

What are the first two parameters that the GroupBy method takes (apart from the source)?

Answer 3

1. Key Selector

2. Element Selector

Question 4

What is the elementSelector parameter used for in a GroupBy method call?

Answer 4

Determining the return type of each element.

Question 5

How do you define a new variable inside a LINQ query expression?

Answer 5

By using the let keyword.

eg. let x = new {y.Name};

Question 6

What is the resultSelector parameter used for in a GroupBy method call?

Answer 6

Determining the data structure to be returned.

Question 7

How do you use a result selector in a LINQ GroupBy query expression?

Answer 7

By using the into keyword after the group/by clause to define a variable that you use in a select clause to determine the return type.

Question 8

What is the keySelector parameter used for in a GroupBy method call?

Answer 8

Determining what value to group the sequence by. This value also becomes the key of each group element.

Question 9

What does the SelectMany extension method do?

Answer 9

It flattens a sequence by allowing us to work with nested sequences.