SelectMany for flattening in C Sharp (C#) - Mini Project: Build & Apply

Using SelectMany to Flatten Nested Lists

📖 Scenario: Imagine you have a list of classrooms, and each classroom has a list of students. You want to get a single list of all students from all classrooms combined.

🎯 Goal: Build a C# program that uses SelectMany to flatten a list of student lists into one list of all students.

📋 What You'll Learn

Create a list of classrooms where each classroom is a list of student names (strings).

Create a variable to hold all students flattened into one list using SelectMany.

Print the flattened list of all students.

💡 Why This Matters

🌍 Real World

Flattening nested collections is common when working with grouped data, like classrooms with students or departments with employees.

💼 Career

Understanding how to flatten collections with SelectMany is useful for data processing, reporting, and simplifying complex data structures in C# applications.

1

Create the nested list of classrooms

Create a variable called classrooms that is a List<List<string>> with exactly these three classrooms:
1. "Alice", "Bob"
2. "Charlie", "David"
3. "Eve", "Frank"

C Sharp (C#)

// Your code here

Need a hint?

Use List<List<string>> and initialize it with three inner lists of strings.

2

Add a variable to hold the flattened list

Create a variable called allStudents of type IEnumerable<string> but do not assign it yet.

C Sharp (C#)

using System.Collections.Generic;

List> classrooms = new List>
{
    new List { "Alice", "Bob" },
    new List { "Charlie", "David" },
    new List { "Eve", "Frank" }
};

// Declare allStudents variable here
// Your code here

Need a hint?

Use IEnumerable<string> to declare allStudents without assigning it yet.

3

Use SelectMany to flatten the classrooms

Assign allStudents to the result of using SelectMany on classrooms to flatten all inner lists into one sequence of strings.

C Sharp (C#)

using System.Collections.Generic;
using System.Linq;

List> classrooms = new List>
{
    new List { "Alice", "Bob" },
    new List { "Charlie", "David" },
    new List { "Eve", "Frank" }
};

// Assign allStudents using SelectMany to flatten classrooms
// Your code here

Need a hint?

Use classrooms.SelectMany(classroom => classroom) to flatten the list.

4

Print the flattened list of all students

Use a foreach loop to print each student in allStudents on its own line.

C Sharp (C#)

using System.Collections.Generic;
using System.Linq;

List> classrooms = new List>
{
    new List { "Alice", "Bob" },
    new List { "Charlie", "David" },
    new List { "Eve", "Frank" }
};

IEnumerable allStudents = classrooms.SelectMany(classroom => classroom);

// Print each student in allStudents
// Your code here

Need a hint?

Use foreach (string student in allStudents) and Console.WriteLine(student) inside the loop.