Is a Bag a Data Structure?


Larry Thompson

Is a Bag a Data Structure?

When it comes to data structures, there are several commonly known ones like arrays, linked lists, stacks, queues, and trees. However, you may have also come across the term “bag” as a data structure.

But what exactly is a bag and how does it differ from other data structures? Let’s dive in and find out!

What is a Bag?

A bag is a type of data structure that stores a collection of items without any particular order or sequence. It is also referred to as a multiset or unordered collection. Unlike other data structures like arrays or linked lists, bags do not enforce any specific organization or arrangement of elements.

One key characteristic of a bag is that it allows duplicate elements. This means that you can have multiple occurrences of the same item in the bag. For example, if we have a bag with the elements [1, 2, 2, 3], we can see that the number 2 appears twice.

Bag Operations

Similar to other data structures, bags also support certain operations for manipulating the collection of items:

  • Add: This operation allows us to add an item to the bag.
  • Remove: With this operation, we can remove an item from the bag.
  • Contains: This operation checks whether an item is present in the bag or not.
  • Size: Returns the total number of items in the bag.

Bags are particularly useful when you want to keep track of counts or frequencies of different elements in a collection. For example, you might want to count how many times a particular word appears in a text document. In such cases, a bag can be a convenient choice.

Implementation of a Bag

There are several ways to implement a bag, depending on the programming language or the specific requirements of your application. One common approach is to use an associative container, such as a dictionary or hash table, where the items are stored as keys and their counts are maintained as values.

Another way to implement a bag is by using an array or list structure and keeping track of the count for each item separately. This approach requires searching through the entire collection when performing operations like add or remove.


Let’s consider an example implementation of a bag using Python:

# Create an empty bag
bag = {}

# Add items to the bag
bag['apple'] = 3
bag['banana'] = 2
bag['orange'] = 5

# Remove an item from the bag
del bag['banana']

# Print the contents of the bag
for item in bag:
    print(item, ":", bag[item])

In this example, we create a dictionary called “bag” and add different fruits with their respective counts. We then remove the banana from the bag and print out the remaining items along with their counts.


A bag is indeed a data structure that allows us to store and manipulate collections of items without any specific order. It is particularly useful when we need to keep track of counts or frequencies of elements. With its flexible nature, bags provide an efficient solution for various scenarios where strict organization is not required.

So next time you encounter the term “bag” in computer science discussions, you’ll know that it refers to an unordered collection that allows duplicates and serves its own unique purpose in the world of data structures.

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