OrderBy and sorting in C Sharp (C#) - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the OrderBy method do in C#?

The OrderBy method sorts a collection in ascending order based on a key you specify. It returns a new sorted sequence without changing the original collection.

beginner

How do you sort a list of numbers in descending order using LINQ?

Use OrderByDescending method. For example: numbers.OrderByDescending(n => n) sorts numbers from largest to smallest.

intermediate

What is the difference between OrderBy and ThenBy?

OrderBy sorts the collection by the first key. ThenBy is used to sort by a second key when the first keys are equal, allowing multi-level sorting.

beginner

Can OrderBy modify the original list?

No, OrderBy does not change the original list. It returns a new sorted sequence. To change the original list, you can use List.Sort().

beginner

How do you sort a list of objects by a property using OrderBy?

You provide a lambda expression that selects the property. For example, people.OrderBy(p => p.Age) sorts people by their Age property in ascending order.

Which method sorts a collection in ascending order by a key in C#?

A Reverse

B OrderByDescending

C ThenByDescending

D OrderBy

OrderBy sorts in ascending order. OrderByDescending sorts in descending order.

What does ThenBy do in sorting?

A Sorts by a second key when the first keys are equal

B Sorts the collection by the first key

C Reverses the order of the collection

D Filters the collection

ThenBy is used for secondary sorting after OrderBy.

Does OrderBy change the original list?

A Yes, it modifies the original list

B No, it returns a new sorted sequence

C Only if you call <code>ToList()</code>

D Only for arrays

OrderBy returns a new sorted sequence and does not modify the original collection.

How do you sort a list of strings in descending order?

A list.OrderByDescending(s =&gt; s)

B list.OrderBy(s =&gt; s)

C list.ThenBy(s =&gt; s)

D list.SortDescending()

OrderByDescending sorts in descending order.

Which method would you use to sort a list of objects by their Name property?

A list.Sort()

B list.OrderBy(o =&gt; o.Age)

C list.OrderBy(o =&gt; o.Name)

D list.Reverse()

Use OrderBy with a lambda selecting the Name property.

Explain how to sort a list of objects by multiple properties using LINQ.

Think about how to chain sorting methods.

Describe the difference between OrderBy and List.Sort().

Consider whether the original list changes.