How to Remove Duplicate Key Values in Bash While Preserving Order

Описание: Discover a simple solution to combine two files in Bash, removing duplicate key values while preserving the original order. Learn effective techniques using script examples.
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This video is based on the question https://stackoverflow.com/q/63954081/ asked by the user 'Suraj Muraleedharan' ( https://stackoverflow.com/u/2258205/ ) and on the answer https://stackoverflow.com/a/63956511/ provided by the user 'Ed Morton' ( https://stackoverflow.com/u/1745001/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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How to Remove Duplicate Key Values in Bash While Preserving Order

When working with files in Bash, you may occasionally face the challenge of merging multiple files while ensuring that any duplicate key values are removed. Preserving the order of the original files can also be important, especially when the order of elements holds significance in your data analysis or processing.

In this post, we will tackle a specific problem: merging two files to create a third file that contains unique key-value pairs without duplicating keys, all while maintaining the order from the original files.

The Challenge

Imagine you have two files, File 1 and File 2, as shown below:

File 1

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File 2

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Your goal is to merge these two files into a third one (File 3) such that it looks like this:

File 3

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Notice that:

The keys from File 1 are preserved in their original order.

If a key from File 2 appears in File 1, its value should be updated to the one from File 2, but only once.

The Solution

Instead of using overly complicated solutions, we can accomplish this task with a straightforward awk script. Here’s how:

Create the awk script: We will write an awk script that processes both files. Let’s call this script tst.awk.

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Let's break down what this script does:

Initialization: Sets field separators to = for key-value pairs and prepares to store keys.

Processing File 1: Each key-value pair from the first file is stored in an array for future use.

Processing File 2: If a key matches one in the first file, its value is updated, and the original key-value pair is printed out.

Final Output Loop: After processing both files, any remaining keys from File 2 are printed.

Run the Script: Execute the awk script with File 2 and File 1 as input.

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Expected Output

When you run the above command, you should receive the following output:

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This output clearly matches our expectations—it combines the keys and preserves their order correctly, removing duplicates along the way.

Conclusion

Merging files while removing duplicate key values and preserving their order can initially seem like a daunting task, but with the right approach using awk, we can achieve it quite simply. The beauty of this method lies in its clarity and efficiency, making it easy to understand and explain to others.

If you have similar needs or further questions, feel free to comment below or explore additional scripts for more complex data manipulations. Happy coding!