Скачать или смотреть How to Stream GroupBy to Nested Maps with Casting in Java

Learn how to effectively group data stored in nested Maps by gender using Java Streams. This post makes it easy to understand the process, even if you're dealing with Object types.
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This video is based on the question https://stackoverflow.com/q/68770217/ asked by the user 'Sheel' ( https://stackoverflow.com/u/2370769/ ) and on the answer https://stackoverflow.com/a/68770784/ provided by the user 'Eritrean' ( https://stackoverflow.com/u/5176992/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Stream GroupBy to Nested Maps with Casting in Java

Data handling is a crucial part of programming, especially in Java when working with nested collections. In this guide, we will tackle a common problem involving Java Streams where you need to calculate totals based on gender from a complex, nested Map structure.

The Challenge

You have a nested set of Maps that stores counts of male and female data for different years, but the data is stored as Object. This presents a challenge when trying to extract the required information using Java Streams.

The main question here is: How do we stream a nested Map and collect totals by gender while handling casting of Object types?

Here’s the structure you’re dealing with:

[[See Video to Reveal this Text or Code Snippet]]

The Solution

To solve this challenge, we’ll utilize Java Streams effectively to group the counts by gender. Below is a proposed solution that will help you achieve the desired output.

Step-by-Step Breakdown

Stream the map values: Start by streaming the values from the total Map. This gives us access to our nested structures.

Cast to Maps: Use a map operation to cast each value to a Map<String, Object> type.

Extract the entry sets: Find the entry set for each map in order to get to the nested male and female counts.

Collect Totals: Utilize Collectors.toMap to aggregate sums for each gender:

Filter each entry's values to keep only those that are instances of Integer.

Map the filtered values to their integer equivalents and sum them up.

Here is the final code snippet that achieves this:

[[See Video to Reveal this Text or Code Snippet]]

Expected Output

By executing this code, you will get a result like this:

[[See Video to Reveal this Text or Code Snippet]]

Final Thoughts

While dealing with nested Maps in Java can be challenging, especially when you need to handle different types, leveraging the power of Java Streams can lead to elegant solutions. However, if you find yourself frequently needing to manage complex structures like this, consider modeling your data in more defined classes. This not only enhances readability but also simplifies your data manipulation processes.

Feel free to ask if you have questions about this solution or if you face any issues with your implementation!