Mastering Data Aggregation and Data Streams with JSON in JavaScript

Coding Interview Prep for Senior Engineers in JavaScript

Practicing Intermediate Implementation and Data StreamsLesson 3

Lesson 3

Mastering Data Aggregation and Data Streams with JSON in JavaScript

Introduction

Welcome to our lesson on mastering data aggregation and data streams with JSON formatting in JavaScript. In this lesson, we'll start by building a basic sales records aggregator. 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 able to manage and format data streams efficiently.

Starter Task Methods and Their Definitions

To begin, we'll implement a basic sales record aggregator. Here are the methods we'll be focusing on:

add_sale(sale_id, amount) - Adds a sale record with a unique identifier sale_id and an amount. If a sale with the same sale_id already exists, it updates the amount.
get_sale(sale_id) - Retrieves the sale amount associated with the sale_id. If the sale does not exist, it returns undefined.
delete_sale(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.

Starter Task Solution

Here is the complete code for the starter task:

JavaScript
1class SalesAggregator {
2    constructor() {
3        this.sales = {};  // Initialize an empty object to store sales records.
4    }
5
6    add_sale(sale_id, amount) {
7        this.sales[sale_id] = amount;  // Add or update the sale with the provided sale_id and amount.
8    }
9
10    get_sale(sale_id) {
11        // Retrieve and return the sale amount for the given sale_id, or undefined if it doesn't exist.
12        return this.sales[sale_id] !== undefined ? this.sales[sale_id] : undefined;
13    }
14
15    delete_sale(sale_id) {
16        if (sale_id in this.sales) {
17            delete this.sales[sale_id];  // Remove the sale record.
18            return true;  // Return true indicating the sale was deleted.
19        }
20        return false;  // Return false if the sale_id doesn't exist.
21    }
22}
23
24// Example Usage
25const aggregator = new SalesAggregator();
26
27// Add sales
28aggregator.add_sale('001', 100.50);
29aggregator.add_sale('002', 200.75);
30
31// Get sale
32console.log(aggregator.get_sale('001'));  // Output: 100.5
33
34// Delete sale
35console.log(aggregator.delete_sale('002'));  // Output: true
36console.log(aggregator.get_sale('002'));  // Output: undefined

Explanation:

The constructor method initializes an empty object to store sales records.
The add_sale method adds a new sale or updates the amount for an existing sale ID.
The get_sale method retrieves the amount for a given sale ID or returns undefined if the sale does not exist.
The delete_sale method 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.

New Methods and Their Definitions

To increase the complexity and usefulness of our sales aggregator, we'll adjust some existing methods and introduce some new methods and functionalities involving JSON.

add_sale(sale_id, amount, date) - Adds or updates a sale record with a unique identifier sale_id, amount, and a date in the format "YYYY-MM-DD".
aggregate_sales(min_amount = 0) - Returns an object with the total number of sales and the total amount of sales where the sale amount is above min_amount. The object format looks like this:
```
JavaScript
1{
2    total_sales: 0,
3    total_amount: 0.0
4}
```
format_sales(min_amount = 0) - Returns the sales data, filtered by min_amount, formatted as JSON. Includes aggregated sales statistics in the output.
get_sales_in_date_range(start_date, end_date) - 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.

Step 1: Enhancing the `add_sale` Method to Include Date

We'll first modify the add_sale method to accept a date.

JavaScript
1add_sale(sale_id, amount, date) {
2    // Add or update the sale with the provided sale_id, amount, and date.
3    this.sales[sale_id] = { amount: amount, date: date };
4}

This ensures that each sale record includes a date in addition to the amount.

Step 2: Implementing the `aggregate_sales` Method

Now, we create the aggregate_sales method:

JavaScript
1aggregate_sales(min_amount = 0) {
2    let total_sales = 0;
3    let total_amount = 0.0;
4    for (const sale of Object.values(this.sales)) {
5        if (sale.amount > min_amount) {
6            total_sales += 1;  // Increment total sales count.
7            total_amount += sale.amount;  // Add to the total amount.
8        }
9    }
10    return { total_sales: total_sales, total_amount: total_amount };  // Return the aggregated results.
11}
12
13// Create an instance of SalesAggregator
14const aggregator = new SalesAggregator();
15
16// Add sales with date
17aggregator.add_sale('001', 100.50, '2023-01-01');
18aggregator.add_sale('002', 200.75, '2023-01-15');
19
20// Aggregate sales
21console.log(aggregator.aggregate_sales(50)); 
22// Output: { total_sales: 2, total_amount: 301.25 }

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

Step 3: Implementing the `format_sales` Method

Next, we'll create the format_sales method to output data in JSON format.

JavaScript
1format_sales(min_amount = 0) {
2    // Filter and format sales data based on min_amount.
3    const filtered_sales = Object.entries(this.sales)
4        .filter(([_, sale]) => sale.amount > min_amount)
5        .map(([sale_id, sale]) => ({ sale_id: sale_id, amount: sale.amount, date: sale.date }));
6
7    // Aggregate sales statistics.
8    const statistics = this.aggregate_sales(min_amount);
9
10    // Combine sales data and statistics into the final result.
11    const result = {
12        sales: filtered_sales,
13        statistics: statistics
14    };
15    return JSON.stringify(result);  // Convert the result to JSON.
16}
17
18// Format sales to JSON
19console.log(aggregator.format_sales(50));
20// Output: '{"sales":[{"sale_id":"001","amount":100.5,"date":"2023-01-01"},{"sale_id":"002","amount":200.75,"date":"2023-01-15"}],"statistics":{"total_sales":2,"total_amount":301.25}}'

This function formats the sales data as JSON and includes aggregated statistics.

Step 4: Implementing the `get_sales_in_date_range` Method

Finally, let's implement the get_sales_in_date_range method:

JavaScript
1get_sales_in_date_range(start_date, end_date) {
2    const start = new Date(start_date);
3    const end = new Date(end_date);
4    return Object.entries(this.sales)
5        .filter(([_, sale]) => {
6            const sale_date = new Date(sale.date);
7            return sale_date >= start && sale_date <= end;  // Check if the sale is within the date range.
8        })
9        .map(([sale_id, sale]) => {
10            return { sale_id: sale_id, ...sale };  // Return the sale data.
11        });
12}
13
14// Get sales in date range
15console.log(aggregator.get_sales_in_date_range('2023-01-01', '2023-12-31'));
16// Output: [{ sale_id: '001', amount: 100.5, date: '2023-01-01' }, { sale_id: '002', amount: 200.75, date: '2023-01-15' }]

This method retrieves all sales within the specified date range.

Lesson Summary

Congratulations! You've now extended a basic sales aggregator to an advanced one capable of filtering, aggregating, and formatting data in JSON. These skills are crucial for handling data streams efficiently, especially when dealing with large datasets. Feel free to experiment with similar challenges to reinforce your understanding. Well done, and see you in the next lesson!

Enjoy this lesson? Now it's time to practice with Cosmo!

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