How to find Complement of two HashSets

Question

I have two HashSets – setA and setB.

1. How can we find the complement of setA and setB?
2. Is the code for intersection the best way to find intersection?

CODE

 string stringA = "A,B,A,A";
 string stringB = "C,A,B,D";

 HashSet<string> setA = new HashSet<string>(stringA.Split(',').Select(t => t.Trim()));
 HashSet<string> setB = new HashSet<string>(stringB.Split(',').Select(t => t.Trim()));

 //Intersection - Present in A and B
 HashSet<string> intersectedSet = new HashSet<string>( setA.Intersect(setB));

 //Complemenet - Present in A; but not present in B

UPDATE:

Use OrdianlIgnoreCase for ignoring case sensitvity How to use HashSet<string>.Contains() method in case -insensitive mode?

REFERENCE:

1. What is the difference between HashSet<T> and List<T>?
2. Intersection of multiple lists with IEnumerable.Intersect()
3. Comparing two hashsets
4. Compare two hashsets?
5. Quickest way to find the complement of two collections in C#

Answer 1

1 - How can we find the complement of setA and setB?

Use HashSet<T>.Except Method

//Complemenet - Present in A; but not present in B
HashSet<string> ComplemenetSet = new HashSet<string>(setA.Except(setB));

try it with following string.

string stringA = "A,B,A,E";
string stringB = "C,A,B,D";

ComplementSet will contain E

2 - Is the code for intersection the best way to find intersection?

Probably, YES

Answer 2

You can use Except to get the complement of A or B. To get a symmetric complement, use SymmetricExceptWith.

setA.SymmetricExceptWith(setB);

Note that this modifies setA. To get the intersection, there are two methods: Intersect, which creates a new HashSet, and IntersectWith, which modifies the first:

// setA and setB unchanged
HashSet<string> intersection = setA.Intersect(setB);

// setA gets modified and holds the result
setA.IntersectWith(setB);