MongoDB $ln Operator

MongoDB provides different types of arithmetic expression operators that are used in the aggregation pipeline stages and $ln operator is one of them. This operator is used to find the natural logarithm of a number and returns the result as a double. 

Syntax: 

{ $ln: <number> }

Here, the number is a valid expression until it resolves to a non- negative number. 

• If the entered value is null, then this operator will return null.
• If the entered value is NaN, then this operator will return NaN.
• If the entered value is a missing field, then this operator will return null.

Examples:

In the following examples, we are working with:

Database: GeeksforGeeks

Collection: example

Document: two documents that contain the details of the shapes in the form of field-value pairs.

Using $ln operator:

In this example, we are going to find the natural logarithm of the value of the side field in the square document.

db.example.aggregate([{$match:{name: "Square"}},
... {$project: {side: 1, naturalLog:{$ln: "$side"}}}])

Using $ln operator in the embedded document: 

In this example, we are going to find the natural logarithm of the value of the measurement.height field in the rectangle document. 

db.example.aggregate([{$match:{name: "Rectangle"}},
... {$project: {"measurement.height": 1, 
      naturalLog: {$ln: "$measurement.height"}}}])