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$ln (aggregation)

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  • Definition
  • Behavior
  • Example
$ln

Calculates the natural logarithm ln (i.e log e) of a number and returns the result as a double.

$ln has the following syntax:

{ $ln: <number> }

The <number> expression can be any valid expression as long as it resolves to a non-negative number. For more information on expressions, see Expression Operators.

$ln is equivalent to $log: [ <number>, Math.E ] expression, where Math.E is a JavaScript representation for Euler's number e.

The default return type is a double. If at least one operand is a decimal, then the return type is a decimal.

If the argument resolves to a value of null or refers to a field that is missing, $ln returns null. If the argument resolves to NaN, $ln returns NaN.

Example
Results
{ $ln: 1 }
0
{ $ln: Math.E } where Math.E is a JavaScript representation for e.
1
{ $ln: 10 }
2.302585092994046

A collection sales contains the following documents:

{ _id: 1, year: "2000", sales: 8700000 }
{ _id: 2, year: "2005", sales: 5000000 }
{ _id: 3, year: "2010", sales: 6250000 }

The following example transforms the sales data:

db.sales.aggregate( [ { $project: { x: "$year", y: { $ln: "$sales" } } } ] )

The operation returns the following results:

{ "_id" : 1, "x" : "2000", "y" : 15.978833583624812 }
{ "_id" : 2, "x" : "2005", "y" : 15.424948470398375 }
{ "_id" : 3, "x" : "2010", "y" : 15.648092021712584 }

Tip

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