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Table of Contents
Basic representation of collections
Common collection operations
Application of collections in practice
Home Java javaTutorial What is a Set?

What is a Set?

Jul 01, 2025 am 01:15 AM
gather math

Sets are the basic structures composed of different objects in mathematics, and their core characteristics are the disorder and uniqueness of elements. 1. The elements in the set have no order, and each element can only appear once; 2. The set is usually represented by uppercase letters, and the elements are represented by lowercase letters or other symbols. Common representation methods include enumeration and description; 3. Common set operations include union (merging and deduplication), intersection (common elements), difference (removing part elements) and subsets (including relationships); 4. Collections are widely used in practice, such as object classification, Set data structures in programming languages, and database query scenarios.

What is a Set?

Sets (Set) are a basic concept in mathematics. Simply put, they are a combination of clear and different objects . These objects can be numbers, letters, colors, or even other sets, collectively referred to as "elements" or "members".

for example:

  • A basket full of different fruits can be regarded as a collection, with apples, bananas, and oranges inside them being their elements.
  • Common examples in mathematics are {1, 2, 3} or {red, green, blue}.

The key features of the collection are:

  • Disorder : There is no order in the elements in the set, {1, 2, 3} and {3, 2, 1} are the same set.
  • Uniqueness : Each element can only appear once in the set, and even if you write it multiple times, it is only counted as one.

Basic representation of collections

Sets are usually represented by uppercase letters, such as A, B, and C, while elements are represented by lowercase letters or other symbols. There are two common representations:

  • Listing method : list all elements and write them in curly braces. For example: A = {1, 2, 3}
  • Descriptive method : defines a set by describing the common features of elements. For example: B = {x | x is a positive even number less than 10}

The description method is more suitable for situations where there are many elements or regularity.

Common collection operations

Sets are not only used to "load things", but also perform some basic operations that are very common in mathematics and computer science:

  • Union : merge two sets to remove duplicate elements. Remembered as A ∪ B
  • Intersection : A set of elements shared by two sets. Remembered as A ∩ B
  • Difference : Remove elements from another set from one set. Remembered as A - B
  • Subset : If all elements in set A are in set B, then A is a subset of B, denoted as A ? B

Let's give a simple example:

  • A = {1, 2, 3}
  • B = {3, 4, 5}

So:

  • A ∪ B = {1, 2, 3, 4, 5}
  • A ∩ B = {3}

Application of collections in practice

The concept of collection looks abstract, but in fact it is often used in our daily lives, but it is just not realized:

  • Organize items : For example, if you sort your clothes by season, the clothes for each season are a collection.
  • Programming languages : Many programming languages ??have Set data structures that are used to store non-duplicate data, such as Set in JavaScript.
  • Database query : Set-like operations are often used in the database to process the intersection, union, etc. of data.

For example, in JavaScript you can create a Set like this:

 let mySet = new Set([1, 2, 3, 2]);
console.log(mySet); // Output: Set {1, 2, 3}

You will find that the duplicate 2 retains only one, which is exactly the characteristic of Set.


Basically that's it. Although the concept of sets is simple, they are very basic and important in the fields of mathematics, logic, programming, etc. Understanding it can help you better organize information and process data.

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