Topic Overview and Importance

Hello and welcome! Today, we're exploring practical data manipulation techniques in C++. We'll use vectors and maps from the C++ Standard Template Library (STL) to represent our data and perform projection, filtering, and aggregation. And here's the star of the show: our operations will be neatly packaged within a C++ class! No mess, all clean code.

Introduction to Data Manipulation

Data manipulation is akin to being a sculptor but for data. We chisel and shape our data to get the desired structure. C++ vectors and maps are perfect for this, and our operations will be conveniently bundled inside a C++ class. So, let's get our toolbox ready! Here's a simple C++ class, DataStream, that will serve as our toolbox:

#include <vector>
#include <map>
#include <string>
#include <iostream>
#include <functional>

class DataStream {
public:
    DataStream(const std::vector<std::map<std::string, std::string>>& data) : data(data) {}

private:
    std::vector<std::map<std::string, std::string>> data;
};
Data Projection in Practice

Our first stop is data projection. Think of it like capturing a photo of our desired features. Suppose we have data about people. If we're only interested in names and ages, we project our data to include just these details. We'll extend our DataStream class with a project method for this:

#include <vector>
#include <map>
#include <string>
#include <iostream>
#include <functional>

class DataStream {
public:
    DataStream(const std::vector<std::map<std::string, std::string>>& data) : data(data) {}

    DataStream project(std::function<std::map<std::string, std::string>(const std::map<std::string, std::string>&)> projectFunc) const {
        std::vector<std::map<std::string, std::string>> projectedData;
        for (const auto& entry : data) {
            projectedData.push_back(projectFunc(entry));
        }
        return DataStream(projectedData);
    }

    void printData() const {
        for (const auto& entry : data) {
            for (const auto& pair : entry) {
                std::cout << pair.first << ": " << pair.second << ", ";
            }
            std::cout << std::endl;
        }
    }

private:
    std::vector<std::map<std::string, std::string>> data;
};

// Let's use it!
int main() {
    DataStream ds({
         { {"name", "Alice"}, {"age", "25"}, {"profession", "Engineer"} },
         { {"name", "Bob"}, {"age", "30"}, {"profession", "Doctor"} }
    });

    DataStream projectedDs = ds.project([](const std::map<std::string, std::string>& entry) {
        return std::map<std::string, std::string>{{"name", entry.at("name")}, {"age", entry.at("age")}};
    });
    projectedDs.printData();
    // Outputs:
    // name: Alice, age: 25,
    // name: Bob, age: 30,
    return 0;
}

As you can see, we now have a new vector with just the names and ages!

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