Jq With_entries To Change Value Of Key Example

jq with_entries to Change the Value of a Key: Examples and Best Practices

This article explores the powerful with_entries function in jq, demonstrating how to modify the values associated with specific keys within JSON objects. We'll cover various scenarios, from simple value transformations to more complex conditional logic, all while focusing on practical examples and best practices for efficient and readable code. This is crucial for data manipulation tasks within pipelines and scripts. Understanding jq with_entries can significantly improve your JSON processing workflows.

What is with_entries?

The with_entries filter in jq allows you to iterate over the key-value pairs of a JSON object. For each entry, you can access both the key (key) and value (value) allowing for manipulation before reconstructing the object. This is incredibly useful when you need to selectively modify specific values based on their keys or their content.

Basic Value Transformation

Let's start with a simple example. Suppose we have a JSON object representing a product:

{
  "productName": "Awesome Widget",
  "price": 29.99,
  "quantity": 10
}

We want to increase the price by 10%. We can achieve this using with_entries:

jq 'with_entries(.value = if .key == "price" then .value * 1.1 else .value end)' input.json

This command iterates through each entry. If the key is "price", it multiplies the value by 1.1 (increasing it by 10%). Otherwise, it leaves the value unchanged.

Conditional Value Changes based on Value Content

with_entries is particularly powerful when combined with conditional statements based on the value itself. For instance, let's say we want to convert string values representing numbers to actual numbers:

{
  "id": "123",
  "name": "Example Item",
  "cost": "45.67"
}

We can use tonumber within with_entries:

jq 'with_entries(.value = if type(.value) == "string" and (.value | tonumber) then .value | tonumber else .value end)' input.json

This checks if the value is a string and if it can be converted to a number using tonumber. If both conditions are true, it performs the conversion; otherwise, it keeps the original value.

Handling Arrays within Objects

Consider a JSON object containing an array:

{
  "items": [
    {"name": "Item A", "price": 10},
    {"name": "Item B", "price": 20}
  ]
}

To add a 5% tax to each item's price, we need to nest map within with_entries:

jq 'with_entries(.value |= if .key == "items" then map(.price *= 1.05) else . end)' input.json

Here, if the key is "items", we use map to iterate over the array and modify the price of each item.

Advanced Techniques and Best Practices

• Error Handling: Always consider potential errors, such as unexpected data types. Use try and catch to handle situations gracefully.
• Readability: Break down complex expressions into smaller, more manageable parts using variables or helper functions.
• Testing: Test your jq expressions thoroughly with various input data to ensure correctness.

jq with_entries is an essential tool for sophisticated JSON manipulation. By mastering its use with conditional logic and array handling, you can significantly streamline your data processing pipelines and create more robust and efficient scripts. Remember to prioritize readability and thorough testing for maintainable and reliable code.