When working with a 2D vector of custom objects, it might be necessary to count the occurrences of a specific attribute across all objects in the vector. This can be useful in scenarios where you need to analyze or manipulate data based on the frequency of a certain attribute.

Here’s an example scenario: let’s say we have a 2D vector myVector of Person objects, and each Person object has an attribute age. We want to count how many times each age appears in the vector.

To accomplish this, we can use a std::map to store the counts for each age value. The std::map will associate each age with its occurrence count.

#include <iostream>
#include <vector>
#include <map>

struct Person {
    std::string name;
    int age;
};

int main() {
    std::vector<std::vector<Person>> myVector = {
        {{ "Alice", 20 }, { "Bob", 30 }, { "Charlie", 20 }},
        {{ "Dave", 25 }, { "Eve", 30 }, { "Frank", 30 }},
        {{ "Grace", 20 }, { "Henry", 25 }}
    };

    std::map<int, int> ageCount; // Map to store age counts

    for (const auto& row : myVector) {
        for (const auto& person : row) {
            ageCount[person.age]++; // Increment count for each age
        }
    }

    // Display the counts
    for (const auto& pair : ageCount) {
        std::cout << "Age " << pair.first << ": " << pair.second << " occurrences\n";
    }

    return 0;
}

In this code, we initialize the 2D vector myVector with some sample data containing multiple rows of Person objects. Then, we define a std::map named ageCount to store the counts for each age.

We use nested for loops to iterate over each Person object in myVector and update the corresponding age count in ageCount. The expression ageCount[person.age]++ retrieves the count associated with the current age and increments it.

Finally, we display the age counts by iterating over the ageCount map and printing each age and its occurrence count.

By using this approach, you can easily count the occurrences of a specific attribute within a 2D vector of custom objects, enabling you to perform further analysis or operations on the data based on these counts.

#cpp #codingtips