Using jq to merge arrays inside merged objects

2 min read 23-09-2024

Using jq to merge arrays inside merged objects

In the world of data processing and manipulation, jq is a powerful tool for working with JSON data. One common task you might encounter is merging arrays that are nested inside JSON objects. In this article, we will discuss how to accomplish this using jq, providing you with practical examples and explanations that will enhance your understanding of the tool.

Problem Scenario

Let’s say you have the following JSON input that consists of multiple objects, each containing an array of items:

[
  {
    "name": "Object1",
    "items": [1, 2, 3]
  },
  {
    "name": "Object2",
    "items": [4, 5]
  },
  {
    "name": "Object3",
    "items": [6, 7, 8]
  }
]

Your goal is to merge the items arrays from these objects into a single array.

jq Code to Merge Arrays

To achieve this with jq, you can use the following command:

jq '[.[] | .items[]]' input.json

Explanation of the jq Command

[.[]: This part iterates over each object in the input array.
| .items[]: For each object, it accesses the items array and expands it, effectively flattening the arrays.
[: Finally, we wrap everything in brackets to collect all items into a new array.

Result

When you run the above command, the output will be:

[1, 2, 3, 4, 5, 6, 7, 8]

Practical Example

Use Case in Real-World Applications

Consider a scenario where you have a series of user profiles, and each profile contains an array of favorite books. You may want to combine all the books into a single list for generating recommendations or statistics.

Here's an example of how such data might look:

[
  {
    "user": "Alice",
    "favorites": ["Book A", "Book B"]
  },
  {
    "user": "Bob",
    "favorites": ["Book C"]
  },
  {
    "user": "Charlie",
    "favorites": ["Book D", "Book E", "Book F"]
  }
]

To merge the favorites arrays into a single array, use:

jq '[.[] | .favorites[]]' users.json

Output

The command will yield the following output:

["Book A", "Book B", "Book C", "Book D", "Book E", "Book F"]

Conclusion

Using jq to merge arrays inside merged objects is a straightforward process that significantly enhances your ability to handle and manipulate JSON data. The examples provided in this article should help you get started with this powerful tool.

Additional Resources

jq Manual
jq Playground - An online environment to test your jq commands.
JSON Editor Online - A handy tool for viewing and editing JSON data.

With the skills and knowledge gained from this article, you’ll be well-equipped to tackle various data processing tasks using jq. Happy coding!