How to Select Specific Data in a Large JSON File and Save with the Same Structure

Learn how to efficiently filter and save data from large JSON files using jq while maintaining the original structure.
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How to Select Specific Data in a Large JSON File and Save with the Same Structure

Handling large JSON files can be daunting, especially when you only need specific data. If you find yourself with a massive JSON file and want to filter out just the data you need, you’re in the right place! In this guide, we will guide you step-by-step on how to select specific data from a big JSON file and save the output while preserving its original structure.

The Problem

Imagine you have a hefty JSON file (around 3GB) that looks like this:

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

You want to filter this data such that only entries with ZIP codes belonging to a specified list are retained, for example:

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

The challenge is to extract this filtered data while ensuring that the output maintains the same structure as the input.

The Solution

1. Simple Solution (If Your Computer Has Enough RAM)

If your system has sufficient RAM, filtering can be done quite simply using the jq command-line tool which is specialized for parsing JSON data. You can use this command:

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

This line of code does the following:

Accesses the listPoint array.

Maps through each entry and selects only those entries whose ZIP code is in the specified whitelist.

2. Streaming Parser (If RAM is Limited)

In cases where your computer cannot handle the entire file in memory, you can employ jq’s streaming capabilities with a two-step approach:

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

Explanation:

The first part generates a stream of relevant JSON objects.

The second part reconstructs these objects into the desired structure.

3. Handling Large Intermediate Results

If the filtered entries still exceed your memory capacity, consider using the following solution:

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

Here, this command constructs the output gradually, which helps manage memory usage more effectively.

4. Selecting ZIP Codes from a Whitelist

If you need to filter the ZIP codes based on a specific whitelist, modify the selection criterion as follows:

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

This allows you to specify which ZIP codes are acceptable based on a predefined list.

Conclusion

Filtering data from a large JSON file can be challenging, but with jq, it becomes manageable whether you have enough resources or need to handle constraints like limited memory. By following the steps outlined in this guide, you can efficiently extract the information you need while maintaining the original structure of your JSON data.

Remember, for more complex uses, it might be beneficial to explore the functionalities offered by jq further, as it can save a great deal of time and effort when dealing with large data sets.