Welcome to our lesson on mastering data aggregation and data streams with C++. In this lesson, you'll learn to build a basic sales records aggregator using C++'s standard library containers. Then, we'll extend its functionality to handle more complex operations such as filtering, data aggregation, and formatting. By the end of this session, you'll be proficient in managing and formatting data streams efficiently in C++.

To get started, we'll create a simple sales record aggregator in C++. Here are the methods we'll focus on:

• void add_sale(const std::string& sale_id, double amount, const std::string& date); - Adds or updates a sale record with a unique identifier sale_id, amount, and a date in the format "YYYY-MM-DD".

• std::optional<double> get_sale(const std::string& sale_id) const; - Retrieves the sale amount associated with the sale_id. If the sale does not exist, it returns an empty optional.

• bool delete_sale(const std::string& sale_id); - Deletes the sale record with the given sale_id. Returns true if the sale was deleted and false if the sale does not exist.

Are these methods clear so far? Great! Let's now look at how we would implement them.

Here is the complete code for the starter task:

Explanation:

• The sales map stores sale records with sale_id as the key and a pair of amount and date as the value.
• add_sale adds a new sale or updates an existing sale ID.
• get_sale retrieves the amount for a given sale ID or returns std::nullopt if the sale does not exist.
• delete_sale removes the sale record for the given sale ID or returns false if the sale does not exist.

Now that we have our basic aggregator, let's extend it to include more advanced functionalities.

To add complexity and usefulness to our sales aggregator, we'll introduce some additional methods for advanced data aggregation, filtering, and formatting functionalities.

• std::pair<int, double> aggregate_sales(double min_amount = 0) const; - Returns the total number of sales and the total sales amount where the sale amount is above min_amount.

• std::string format_sales(double min_amount = 0) const; - Returns the sales data, filtered by min_amount, formatted as a plain text string. Includes sales statistics in the output.

• std::vector<std::tuple<std::string, double, std::string>> get_sales_in_date_range(const std::string& start_date, const std::string& end_date) const; - Retrieves all sales that occurred within the given date range, inclusive. Each sale includes sale_id, amount, and date.

Let's implement these methods step by step.

We'll create the aggregate_sales method:

This method iterates through the sales and sums those that exceed the min_amount.

Next, we create the format_sales method to output data in plain text format.

In this method, std::ostringstream is used, which is a stream class to operate on strings. It allows you to format strings in a way similar to using std::cout. We append formatted data to the stream using the insertion operators (<<), then use the str() method to retrieve the final concatenated string. This approach is beneficial for creating large and complex strings safely and efficiently.

Let's implement get_sales_in_date_range, which relies on parsing dates and comparing them to filter sales records.

In this implementation, parse_date is a helper lambda function that converts a date string into a std::chrono::system_clock::time_point, allowing you to compare dates. This involves reading the date into a std::tm structure with std::get_time and then converting it to a time_point using std::chrono::system_clock::from_time_t. This functionality is fundamental when working with date ranges to ensure accurate filtering of sales records.

Congratulations! You've extended a basic C++ sales aggregator to an advanced aggregator capable of filtering, aggregating, and formatting data, using custom structures for data handling. These skills are crucial for efficiently managing data streams, especially with large datasets in C++. Feel free to experiment with similar challenges to reinforce your understanding. Well done!