How to Use jq to Find Common Values from Two String Arrays

Discover how to effectively find common values between two string arrays using `jq`, a powerful command-line utility for processing JSON data.
---

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 can I use `jq` to find common values from two string arrays

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
Finding Common Values from Two String Arrays with jq

When working with data in JSON format, it’s common to need to identify common elements between different arrays. Suppose you have two string arrays and want to find which strings from the second array exist in the first one. For example, given the arrays:

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

Your goal is to return ["b"]. This is a straightforward task, but it's essential to know how to use the jq tool correctly to achieve this. In this post, we’ll break down how to solve this problem step by step.

Understanding the Task

Before diving into the solution, let’s clarify what’s happening:

You have two string arrays, arr1 and arr2.

Your aim is to identify which elements from arr2 are also present in arr1.

The expected output is a new array containing only these common elements.

A Common Misstep in jq

When first attempting to solve this problem, you might try using subtraction to identify the differences between the arrays. Here's an example of a common command:

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

Running this command will result in:

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

This output indicates the elements that are present in the first array but absent in the second. However, this is not what you want; you want to find the elements that are present in both arrays.

The Correct Approach

To achieve the desired outcome, we can use the formula that utilizes MATCH, then perform operations to find the intersection of the two arrays. Here’s how to do that:

Step 1: Identify the Elements

The first step is to identify the common elements through subtraction again, but this time with a twist:

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

Step 2: Execution

When you run this command, you will receive the output:

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

Step 3: Explanation of the Output

Inside the parentheses, the command ["a", "b", "c"] - ["b", "d", "1"] finds the elements in arr1 that are not in arr2, resulting in ["a", "c"].

We then subtract this result from arr1 to effectively isolate the common values.

Conclusion

Using jq to find common values between two arrays is manageable with the right approach. By employing the method outlined above, you can efficiently extract the intersection of string arrays without complicated processing.

Feel free to modify the arrays in the examples provided and apply this method to different datasets. Now you know how to find common values in JSON arrays using jq!

If you have further questions or need additional help with jq, leave a comment below and I'll be happy to assist!