How to Sort a 2D ArrayList by Column Value in Java?

Learn how to effectively sort a 2D ArrayList in Java by a specified column and handle cases where values are equal using a secondary column for comparison.
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How to Sort a 2D ArrayList by Column Value in Java?

Working with multidimensional arrays can sometimes be tricky, especially when it comes to sorting them according to specific criteria. A common scenario is needing to sort a two-dimensional ArrayList by the values of a certain column. Moreover, if two rows contain the same value for that column, those rows must then be compared using another column.

In this post, we’ll detail how to accomplish this in Java, providing clear examples along the way.

The Problem

Imagine you have the following ArrayList of Lists that represents a 2D array:

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

You want to sort this list primarily by the value in the first column (index [0]). However, if two rows have the same value at this index, you want to sort those rows using the value from the fourth column (index [3]).

For instance, the output you desire would be:

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

The Solution

To achieve this sorting, you need to modify the Comparator to take into account both indices. Let's break down the solution:

1. Create a Custom Comparator

The sorting process can be managed using a Comparator that defines the order in which the rows should be sorted based on specified indices. Here’s how to adjust your existing Comparator:

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

2. Applying the Comparator with Sorting

You can use this Comparator in your sort function. Here's how you can implement this in both pre-Java 8 and Java 8 or above:

For Java 8 and Above

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

For Pre-Java 8

If you’re using a version of Java prior to Java 8, you can utilize the traditional anonymous class syntax:

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

3. The Output

After applying sorting using either method illustrated above, the resulting sorted ArrayList will be:

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

Conclusion

Sorting a 2D ArrayList by column values in Java may seem daunting at first, but with the right approach using a custom Comparator, you can effectively manage it. By comparing primary column values first and resolving ties with a secondary column, you can ensure that your data is accurately sorted according to your requirements.

Happy coding!