OrderBy and sorting in C Sharp (C#) - Mini Project: Build & Apply

Sorting a List of Products by Price

📖 Scenario: You work in a store and have a list of products with their prices. You want to show the products sorted by their price from lowest to highest.

🎯 Goal: Build a small program that creates a list of products with prices, then sorts them by price using OrderBy, and finally prints the sorted list.

📋 What You'll Learn

Create a list of products with exact names and prices

Create a variable to hold the sorted products using OrderBy

Use a foreach loop to print each product name and price

💡 Why This Matters

🌍 Real World

Sorting products by price helps customers find cheaper or more expensive items easily in online stores or inventory systems.

💼 Career

Sorting and ordering data is a common task in software development, especially in e-commerce, data analysis, and user interface design.

1

Create the list of products

Create a list called products of type List<KeyValuePair<string, double>> with these exact entries: ("Apple", 1.20), ("Banana", 0.50), ("Cherry", 2.00), ("Date", 3.00), ("Elderberry", 1.50).

C Sharp (C#)

using System;
using System.Collections.Generic;

class Program
{
    static void Main()
    {
        // Create the list of products with exact entries here
        
    }
}

Hint

Use new List<KeyValuePair<string, double>> { ... } and add each product with new KeyValuePair<string, double>(name, price).

2

Create a sorted list using OrderBy

Create a variable called sortedProducts that stores the products sorted by price using products.OrderBy(p => p.Value). Add using System.Linq; at the top if needed.

C Sharp (C#)

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

class Program
{
    static void Main()
    {
        List> products = new List>
        {
            new KeyValuePair("Apple", 1.20),
            new KeyValuePair("Banana", 0.50),
            new KeyValuePair("Cherry", 2.00),
            new KeyValuePair("Date", 3.00),
            new KeyValuePair("Elderberry", 1.50)
        };

        // Create sortedProducts using OrderBy here
        
    }
}

Hint

Use var sortedProducts = products.OrderBy(p => p.Value); to sort by the price.

3

Print the sorted products

Use a foreach loop with variables product to iterate over sortedProducts. Inside the loop, print the product name and price using Console.WriteLine($"{product.Key}: {product.Value}").

C Sharp (C#)

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

class Program
{
    static void Main()
    {
        List> products = new List>
        {
            new KeyValuePair("Apple", 1.20),
            new KeyValuePair("Banana", 0.50),
            new KeyValuePair("Cherry", 2.00),
            new KeyValuePair("Date", 3.00),
            new KeyValuePair("Elderberry", 1.50)
        };

        var sortedProducts = products.OrderBy(p => p.Value);

        // Print each product name and price here
        
    }
}

Hint

Use foreach (var product in sortedProducts) and print with Console.WriteLine($"{product.Key}: {product.Value}").

4

Run and see the sorted output

Run the program and observe the output. It should print the products sorted by price from lowest to highest.

C Sharp (C#)

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

class Program
{
    static void Main()
    {
        List> products = new List>
        {
            new KeyValuePair("Apple", 1.20),
            new KeyValuePair("Banana", 0.50),
            new KeyValuePair("Cherry", 2.00),
            new KeyValuePair("Date", 3.00),
            new KeyValuePair("Elderberry", 1.50)
        };

        var sortedProducts = products.OrderBy(p => p.Value);

        foreach (var product in sortedProducts)
        {
            Console.WriteLine($"{product.Key}: {product.Value}");
        }
    }

    // Run the program to see the output
}

Hint

The output should list products sorted by price from lowest to highest.

Practice

1. What does the OrderBy method do in C#?

easy

A. Sorts a collection in ascending order based on a key

B. Deletes elements from a list

C. Reverses the order of elements in a list

D. Filters elements based on a condition

Solution

1. Step 1: Understand the purpose of OrderBy

   The OrderBy method sorts elements in a collection based on a key in ascending order.

2. Step 2: Compare with other options

   Options B, C, and D describe different operations (deletion, reversing, filtering) which OrderBy does not perform.

3. Final Answer:

   Sorts a collection in ascending order based on a key -> Option A

4. Quick Check:

   OrderBy = Sort ascending [OK]

Hint: OrderBy sorts ascending by key, not filtering or deleting [OK]

Common Mistakes:

• Confusing OrderBy with filtering methods like Where
• Thinking OrderBy modifies the original list
• Mixing up OrderBy with reversing or deleting

2. Which of the following is the correct syntax to sort a list of integers named numbers in ascending order using OrderBy?

easy

A. numbers.OrderBy();

B. numbers.OrderBy(n);

C. numbers.OrderBy(n => n);

D. numbers.OrderBy(n => );

Solution

1. Step 1: Check the correct lambda syntax

   OrderBy requires a key selector function like n => n to specify sorting key.

2. Step 2: Validate each option

   numbers.OrderBy(n => n); uses correct lambda syntax. numbers.OrderBy(); misses the key selector. numbers.OrderBy(n); passes a variable, not a lambda. numbers.OrderBy(n => ); has incomplete lambda syntax.

3. Final Answer:

   numbers.OrderBy(n => n); -> Option C

4. Quick Check:

   OrderBy needs a key selector lambda [OK]

Hint: OrderBy always needs a key selector lambda like n => n [OK]

Common Mistakes:

• Omitting the lambda expression inside OrderBy
• Passing a variable instead of a lambda
• Using incomplete or invalid lambda syntax

3. What will be the output of the following code?

var fruits = new List<string> { "banana", "apple", "cherry" };
var sorted = fruits.OrderBy(f => f);
foreach(var fruit in sorted) {
    Console.Write(fruit + " ");
}

medium

A. banana apple cherry

B. apple banana cherry

C. cherry banana apple

D. apple cherry banana

Solution

1. Step 1: Understand the sorting key

   The code sorts the list of fruits alphabetically by their string value.

2. Step 2: Determine the sorted order

   Alphabetically, "apple" comes before "banana", which comes before "cherry".

3. Final Answer:

   apple banana cherry -> Option B

4. Quick Check:

   OrderBy sorts strings alphabetically [OK]

Hint: OrderBy sorts strings alphabetically ascending [OK]

Common Mistakes:

• Assuming original order is preserved
• Confusing OrderBy with OrderByDescending
• Not recognizing alphabetical order

4. The following code throws a compile-time error. What is the mistake?

var numbers = new List<int> { 3, 1, 2 };
var sorted = numbers.OrderBy();

medium

A. numbers must be an array, not a list

B. List<int> cannot be sorted

C. OrderBy should be OrderByDescending

D. OrderBy requires a key selector lambda expression

Solution

1. Step 1: Identify the method signature requirement

   OrderBy requires a key selector function to specify how to sort elements.

2. Step 2: Analyze the error cause

   Calling OrderBy() without any argument causes a compile error because the key selector is missing.

3. Final Answer:

   OrderBy requires a key selector lambda expression -> Option D

4. Quick Check:

   OrderBy needs a lambda key selector [OK]

Hint: Always provide a key selector lambda to OrderBy [OK]

Common Mistakes:

• Calling OrderBy without arguments
• Thinking OrderBy works without a key selector
• Confusing List and array types for sorting

5. Given a list of students with properties Name and Score, how do you sort the list first by Score descending, then by Name ascending using LINQ?

hard

A. students.OrderByDescending(s => s.Score).ThenBy(s => s.Name);

B. students.OrderBy(s => s.Score).OrderBy(s => s.Name);

C. students.OrderBy(s => s.Name).OrderByDescending(s => s.Score);

D. students.OrderByDescending(s => s.Name).ThenByDescending(s => s.Score);

Solution

1. Step 1: Understand multi-level sorting

   To sort by multiple keys, use OrderBy or OrderByDescending for the first key, then ThenBy or ThenByDescending for the next keys.

2. Step 2: Apply correct order and directions

   We want to sort by Score descending first, then by Name ascending, so use OrderByDescending(s => s.Score) followed by ThenBy(s => s.Name).

3. Final Answer:

   students.OrderByDescending(s => s.Score).ThenBy(s => s.Name); -> Option A

4. Quick Check:

   OrderByDescending + ThenBy for multi-level sort [OK]

Hint: Use ThenBy after OrderBy for secondary sorting [OK]

Common Mistakes:

• Using multiple OrderBy calls instead of ThenBy
• Mixing ascending and descending incorrectly
• Sorting by wrong property order