$map Operator in MongoDB

What is $map in MongoDB?

In MongoDB, $map is a powerful aggregation operator that allows for array modifications within documents. It enables developers to easily apply expressions to individual array elements, resulting in a new array with updated values. Data manipulation operations such as computations, filtering, and information extraction become more efficient and simplified by employing a$map. This operator enables developers to design more sophisticated and intelligent applications by enabling flexible and dynamic array modifications. MongoDB users may leverage the full potential of arrays with $map, enabling smooth data processing and analysis in their projects.

Syntax

The syntax for using mapping in MongoDB is as follows:

Parameters

The parameters used in $map syntax are as follows:

• input: It specifies the array to be transformed or processed. This can be an array field of a document, a variable, or the result of an expression.
• as: It can be a string representing the variable name used to access each element in the input array. You can also define a variable representing each element in the input array.
• in: It is an expression that determines the modifications or transformations to be applied to each element. It also specifies the expression to apply to each element, using the defined variable.

Return Values

By doing mapping in MongoDB, it returns a new array that contains the results of applying the specified expression to each element of the input array. The length of the output array matches the length of the input array. Each element in the output array corresponds to the transformed value of the corresponding element in the input array. If an element in the input array is missing or null, the corresponding position in the output array will also be null.

Behavior

When using mapping in MongoDB, each element of the input array is processed individually. The specified expression is applied to transform or modify each element, and the resulting values are stored in the output array. The order of the elements in the output array matches the order of the input array. If an element in the input array is missing or null, the corresponding position in the output array will also be null, maintaining alignment between the arrays.

How to Use $map in MongoDB?

To use mapping in MongoDB, you must incorporate the flow into an aggregation pipeline. Within the pipeline stages, you will utilize the **$map operator** for array transformations. You will then specify the input array to be processed, either an array field or the result of an expression. Afterward, you'll define a variable to represent each element using the **'as'** parameter. Then, specify the expression to apply to each element using the **'in'** parameter. The$map operator enables versatile array modifications such as calculations, filtering, and data extraction. By integrating $map into the aggregation pipeline, you can efficiently transform and manipulate arrays, enhancing data processing capabilities in MongoDB applications.

Examples of $map in MongoDB

Let’s see some examples to understand mapping in MongoDB in a better way.

Example 1: Suppose we have a MongoDB collection named Sets with the following documents:

We want to increment each element in the numbers array by 1 and create a new array called incrementedNumbers. Here's the MongoDB aggregation query using the $map operator:

Output: The output of the aggregation query will be:

As you can see, the $map operator is applied to each element of the numbers array within each document. It increments each element by 1, resulting in a new array called incrementedNumbers. The output documents include the original fields and the newly created incrementedNumbers field, reflecting the modified arrays.

Example 2: Suppose we have a MongoDB collection named students with the following documents:

We want to create a new array called highScores that only includes scores greater than 80. Here's the MongoDB aggregation query using the $map operator:

Output: The output of the aggregation query will be:

As you can see, the $map operator is applied to each element of the scores array within each document. It checks if the score is greater than 80 using the$gt operator. If the condition is true, it keeps the score, otherwise assigns null. The resulting array, highScores, only includes the scores that meet the condition, while the rest are replaced with null.