What Is Multimap Data Structure?


Larry Thompson

Multimap Data Structure: Explained & Explored

The multimap data structure is a powerful tool that allows us to store key-value pairs in an organized and efficient manner. Unlike a regular map or dictionary, a multimap can associate multiple values with the same key. In other words, it allows for duplicate keys and provides a convenient way to manage collections of values under a single key.

Why use a Multimap?

A multimap is particularly useful when we need to handle situations where multiple elements need to be associated with the same key. For example, consider a scenario where we are building an address book application.

Each person can have multiple phone numbers or email addresses associated with their name. Using a multimap, we can easily store and retrieve this information without any hassle.

How does a Multimap work?

A multimap operates on the principle of associating each key with a collection of values. Under the hood, it typically uses a combination of data structures such as binary search trees or hash tables to efficiently store and retrieve the data.

Adding Elements to a Multimap:

When adding elements to a multimap, we specify both the key and value associated with it. As mentioned earlier, unlike regular maps, multiple values can be associated with the same key.

To illustrate this concept, let’s consider an example where we want to store student names along with their respective grades in various subjects:

multimap studentGrades;
studentGrades.insert(make_pair(“John Doe”, 85));
studentGrades.insert(make_pair(“Jane Smith”, 92));
studentGrades.insert(make_pair(“John Doe”, 78));

In this example, “John Doe” has two grades associated with his name. The multimap allows us to store both these grades under the same key.

Retrieving Elements from a Multimap:

To retrieve elements from a multimap, we can use the key as the search criterion. Since multiple values can be associated with the same key, we need to iterate over each value associated with the given key.

Continuing with our previous example, let’s retrieve all the grades for “John Doe”:

multimap::iterator it;
for (it = studentGrades.begin(); it != studentGrades.end(); ++it) {
if (it->first == “John Doe”) {
cout << it->second << endl; } } ``` This code snippet will output both grades associated with "John Doe" (85 and 78).

Removing Elements from a Multimap:

Similar to adding and retrieving elements, removing elements from a multimap is straightforward. We can remove elements based on their keys or specific values associated with those keys.

To remove all entries for “John Doe” from our previous example:

studentGrades.erase(“John Doe”);

This will remove all entries associated with the key “John Doe” from the multimap.


The multimap data structure provides a flexible and efficient way to handle scenarios where multiple values need to be associated with the same key. Its ability to store duplicate keys makes it an ideal choice in situations like contact management or database applications. By leveraging its power, developers can easily manage collections of data in an organized and structured manner.

So, next time you encounter a scenario where you need to store multiple values under a single key, remember the multimap data structure and its versatile capabilities!

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