Скачать или смотреть How to Group Objects by Value Change in Kotlin

Learn how to efficiently group city data by prefecture in Kotlin, transforming JSON responses into a well-structured format.
---
This video is based on the question https://stackoverflow.com/q/63029889/ asked by the user '4ankoku' ( https://stackoverflow.com/u/13974399/ ) and on the answer https://stackoverflow.com/a/63030577/ provided by the user 'youhans' ( https://stackoverflow.com/u/2250391/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: How to group object by value change

Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/l...
The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license.

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
How to Group Objects by Value Change in Kotlin

In the world of application development, you often need to manipulate data received from APIs. One common task is grouping related data based on certain attributes, such as grouping cities by their prefectures. If you're working with Kotlin and have encountered a situation where you need to achieve this, fret not! In this post, we’ll guide you through how to group objects by value change effectively with a practical coding example.

The Challenge

Imagine you receive a JSON response from an API containing information about cities and their associated prefectures. The data structure is as follows:

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

Your goal is to manipulate this data so that it’s grouped by prefectures, resulting in a clean output that displays cities under their respective prefectures. Here's the expected outcome:

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

The Solution

To achieve this, we will use Kotlin’s collection functions, such as groupBy, which allows us to easily group our data. Below is a step-by-step breakdown along with the corresponding code:

Step 1: Define the Data Classes

First, ensure you have the data classes representing your JSON structure:

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

Step 2: Parse the JSON

Next, you need to parse the JSON to a Country object using a library like Jackson:

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

Step 3: Group the Cities by Prefecture

Now, you can group the cities based on their prefectures. The groupBy function allows us to achieve this quickly. Here’s the code to execute this:

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

Step 4: Format the Output

After grouping, the last step is to format the output so that it matches your expectation. Use joinToString to build the final string:

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

Complete Code

Here’s the complete Kotlin code all put together:

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

Conclusion

By following these steps, you can efficiently group objects by value change in Kotlin. This method provides a clear and structured output, which is essential for data readability in applications. Whether you're displaying data to users or manipulating it for further processing, organizing your objects makes a huge difference. Happy coding!