Set operations (Union, Intersect, Except) in C Sharp (C#) - Mini Project: Build & Apply

Set operations (Union, Intersect, Except) in C#

📖 Scenario: You are managing two lists of favorite fruits from two friends. You want to find fruits they both like, fruits either one likes, and fruits only one friend likes.

🎯 Goal: Build a C# program that uses set operations Union, Intersect, and Except on two lists of fruits.

📋 What You'll Learn

Create two lists of strings named friend1Fruits and friend2Fruits with exact fruits given.

Create a variable allFruits that is the union of both lists.

Create a variable commonFruits that is the intersection of both lists.

Create a variable uniqueToFriend1 that contains fruits only in friend1Fruits but not in friend2Fruits.

Print the results exactly as instructed.

💡 Why This Matters

🌍 Real World

Set operations help compare collections like user preferences, inventory lists, or survey answers.

💼 Career

Understanding set operations is useful for data analysis, filtering data, and combining information efficiently in software development.

1

Create the fruit lists

Create two lists of strings called friend1Fruits and friend2Fruits. Set friend1Fruits to contain "apple", "banana", and "cherry". Set friend2Fruits to contain "banana", "dragonfruit", and "apple".

C Sharp (C#)

# Your code here

Hint

Use List<string> and initialize with the exact fruits inside curly braces.

2

Create the union set

Create a variable called allFruits that holds the union of friend1Fruits and friend2Fruits using the Union method and convert it to a list.

C Sharp (C#)

using System.Collections.Generic;

List friend1Fruits = new List { "apple", "banana", "cherry" };
List friend2Fruits = new List { "banana", "dragonfruit", "apple" };

// Your code here

Hint

Use friend1Fruits.Union(friend2Fruits).ToList() to get all unique fruits.

3

Create the intersection and difference sets

Create a variable called commonFruits that holds the intersection of friend1Fruits and friend2Fruits using the Intersect method and convert it to a list. Also create a variable called uniqueToFriend1 that holds fruits only in friend1Fruits but not in friend2Fruits using the Except method and convert it to a list.

C Sharp (C#)

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

List friend1Fruits = new List { "apple", "banana", "cherry" };
List friend2Fruits = new List { "banana", "dragonfruit", "apple" };

List allFruits = friend1Fruits.Union(friend2Fruits).ToList();

// Your code here

Hint

Use Intersect for common fruits and Except for fruits unique to friend1.

4

Print the results

Print the contents of allFruits, commonFruits, and uniqueToFriend1 each on a separate line. Use string.Join(", ", ...) to join the list items. Print exactly as follows:
All fruits: apple, banana, cherry, dragonfruit
Common fruits: apple, banana
Unique to friend1: cherry

C Sharp (C#)

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

List friend1Fruits = new List { "apple", "banana", "cherry" };
List friend2Fruits = new List { "banana", "dragonfruit", "apple" };

List allFruits = friend1Fruits.Union(friend2Fruits).ToList();

List commonFruits = friend1Fruits.Intersect(friend2Fruits).ToList();
List uniqueToFriend1 = friend1Fruits.Except(friend2Fruits).ToList();

// Your code here

Hint

Use Console.WriteLine and string.Join to print the lists as comma-separated strings.

Practice

1.

Which set operation in C# returns all unique elements from two collections combined?

easy

A. Union

B. Intersect

C. Except

D. Concat

Solution

1. Step 1: Understand the meaning of Union

   Union combines all unique elements from both collections without duplicates.

2. Step 2: Compare with other operations

   Intersect returns only common elements, Except returns elements only in the first collection, and Concat just joins collections without removing duplicates.

3. Final Answer:

   Union -> Option A

4. Quick Check:

   Union = all unique elements combined [OK]

Hint: Union = combine all unique items from both sets [OK]

Common Mistakes:

• Confusing Union with Intersect
• Thinking Concat removes duplicates
• Mixing Except with Union

2.

Which of the following is the correct syntax to get the intersection of two sets setA and setB in C#?

var result = ???;

easy

A. setA.Join(setB)

B. setA.Intersect(setB)

C. setA.Except(setB)

D. setA.Union(setB)

Solution

1. Step 1: Identify method for intersection

   The Intersect method returns elements common to both collections.

2. Step 2: Verify syntax correctness

   setA.Intersect(setB) is the correct syntax; Union and Except do different operations, and Join is unrelated.

3. Final Answer:

   setA.Intersect(setB) -> Option B

4. Quick Check:

   Intersect = common elements [OK]

Hint: Use Intersect() to find common elements between sets [OK]

Common Mistakes:

• Using Union instead of Intersect
• Trying to use Join for sets
• Incorrect method call syntax

3.

What is the output of the following C# code?

var setA = new HashSet<int>() {1, 2, 3, 4};
var setB = new HashSet<int>() {3, 4, 5, 6};
var result = setA.Except(setB);
Console.WriteLine(string.Join(",", result));

medium

A. 1,2,5,6

B. 3,4

C. 5,6

D. 1,2

Solution

1. Step 1: Understand Except operation

   Except returns elements in the first set that are not in the second set.

2. Step 2: Apply Except to given sets

   setA has 1,2,3,4; setB has 3,4,5,6; elements in setA but not in setB are 1 and 2.

3. Final Answer:

   1,2 -> Option D

4. Quick Check:

   Except = elements only in first set [OK]

Hint: Except returns items only in first set, not in second [OK]

Common Mistakes:

• Confusing Except with Intersect
• Including elements from second set
• Expecting all unique elements combined

4.

Find the error in this C# code snippet that tries to get the union of two sets set1 and set2:

var set1 = new HashSet<string>() {"apple", "banana"};
var set2 = new HashSet<string>() {"banana", "cherry"};
var result = set1.Union(set2).ToList();
Console.WriteLine(result);

medium

A. Union method does not exist for HashSet

B. ToList() should be called before Union

C. Console.WriteLine cannot print a List directly

D. HashSet cannot contain strings

Solution

1. Step 1: Check method usage

   Union exists and works on HashSet; ToList() is valid after Union.

2. Step 2: Identify Console.WriteLine issue

   Console.WriteLine cannot print a List directly; it prints the type name instead.

3. Final Answer:

   Console.WriteLine cannot print a List directly -> Option C

4. Quick Check:

   Printing List needs string.Join or loop [OK]

Hint: Use string.Join to print collections, not Console.WriteLine directly [OK]

Common Mistakes:

• Assuming Union is invalid for HashSet
• Calling ToList before Union
• Thinking HashSet can't hold strings

5.

You have two lists of integers representing IDs: list1 = {1, 2, 3, 4, 5} and list2 = {4, 5, 6, 7}. You want to find IDs that are either in list1 or list2 but not in both (exclusive or). Which C# code snippet correctly achieves this using set operations?

hard

A. var result = list1.Except(list2).Union(list2.Except(list1));

B. var result = list1.Intersect(list2).Except(list1.Union(list2));

C. var result = list1.Union(list2).Except(list1.Except(list2));

D. var result = list1.Except(list2).Intersect(list2.Except(list1));

Solution

1. Step 1: Understand exclusive or (XOR) logic

   XOR means elements in one set or the other but not both.

2. Step 2: Analyze each option

   var result = list1.Union(list2).Except(list1.Except(list2)); subtracts elements unique to list1 from the union, leaving common and list2-unique elements - incorrect. var result = list1.Except(list2).Union(list2.Except(list1)); combines elements unique to each list using Except and Union, which directly matches XOR.

3. Final Answer:

   var result = list1.Except(list2).Union(list2.Except(list1)); -> Option A

4. Quick Check:

   XOR = unique elements from each set combined [OK]

Hint: XOR = (A except B) union (B except A) [OK]

Common Mistakes:

• Using Intersect instead of Except for uniqueness
• Confusing union and intersection order
• Trying to intersect except results