How to Convert Two Arrays into an Object in MongoDB

Discover how to transform two arrays into an object in MongoDB, allowing for the aggregation of similar values efficiently.
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Introduction

Are you working with MongoDB and faced with the challenge of converting two arrays into an object? If your first array contains duplicate values, this task can seem daunting. In this guide, we'll walk through a practical example and provide you with a clear, detailed solution to achieve this using MongoDB's aggregation framework.

Problem Overview

Suppose you have a collection that includes multiple documents structured like this:

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

Your goal is to transform this collection into a more streamlined format:

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

Solution Breakdown

To achieve the transformation outlined above, we will utilize MongoDB's aggregation pipeline. Below is a step-by-step guide on how to implement this:

Step 1: Create a Range for Indexing

Step 2: Looping Through Arrays

Using the $map operator, loop through the range created in step 1 to simultaneously access elements from both name and value arrays. This way, we will generate an array of key-value pairs ({ k: "", v: "" }).

Step 3: Unwind the Array

Utilize the $unwind stage to deconstruct the newly created array. This prepares the data for grouping.

Step 4: Grouping by Key and Accumulating Values

Next, perform a $group operation to group by the key (field3.k) and accumulate values (field3.v). This step consolidates multiple values under each unique key.

Step 5: Grouping into an Organized Structure

You'll want to group again, this time using null as the identifier to create an aggregated structure of keys and their corresponding values.

Step 6: Concatenate with Other Fields

In this phase, concatenate field1 and field2 with the array from the previous grouping stage, creating a comprehensive listing of keys.

Step 7: Convert Array to Object

Finally, utilize the $arrayToObject operator to convert the assembled array of key-value pairs into an object format.

Example Aggregation Query

Here’s how to piece it all together using a MongoDB aggregation pipeline in the query shell:

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

Expected Output

Executing the above aggregation will yield the following structure:

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

Conclusion

And there you have it! You've successfully converted two arrays into an object in MongoDB using aggregation, even when the first array contained duplicate values. This method streamlines your data and enhances usability for further operations. If you have any questions or run into issues, feel free to leave a comment below!