Multimap stores key-value pairs and for the same key, we can have more than one value i.e. multiple values for a single key. We can use this property of multimap to group vector of pair elements easily. In this article, we will discuss how to group elements of a vector of pairs in a multimap container.
Example
Input: myVector ={ {"A", 80},{"B", 70},{"A", 90},{"C", 90},{"B", 60},{"A", 100}} Output: myMultiMap = { {"A", 80},{"A", 90},{"A", 100},{"B", 60},{"B", 70},{"C", 90}}
Grouping of Vector of Pair Elements
We can just create a multimap of the same type as a pair and insert the vector elements in the map using the insert function. After that, we can access all the key-value pairs with the same key using the std::multimap::equal_range() function.
C++ Program to Group Vector of Pairs Elements in a Multimap
// C++ Program to Demonstrate Multimap and Access All // Key-Value Pairs #include <iostream> #include <map> #include <vector> using namespace std;
int main()
{ // Create a multimap with pairs
multimap< int , string> myMultiMap;
// Insert vector elements into the multimap
vector<pair< int , string> > elements
= { { 1, "Apple" },
{ 2, "Banana" },
{ 1, "Apricot" },
{ 3, "Cherry" },
{ 2, "Blueberry" } };
for ( const auto & element : elements) {
myMultiMap.insert(element);
}
// Access all key-value pairs for all keys
cout << "All Key-Value pairs:" << endl;
for ( const auto & keyValuePair : myMultiMap) {
int key = keyValuePair.first;
auto range = myMultiMap.equal_range(key);
cout << "Key: " << key << endl;
for ( auto it = range.first; it != range.second;
++it) {
cout << " Value: " << it->second << endl;
}
}
return 0;
} |
Output
All Key-Value pairs:
Key: 1
Value: Apple
Value: Apricot
Key: 1
Value: Apple
Value: Apricot
Key: 2
Value: Banana
Value: Blueberry
Key: 2
Value: Banana
Value: Blueberry
Key: 3
Value: Cherry
Time Complexity: O(N log(N))
Auxiliary Space: O(N)