$exp (aggregation)

Definition

$exp

Raises Euler's number (i.e. e ) to the specified exponent and returns the result.

$exp has the following syntax:

{ $exp: <exponent> }

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

Behavior

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, $exp returns null. If the argument resolves to NaN, $exp returns NaN.

Example

A collection named accounts contains the following documents:

db.accounts.insertMany( [
   { _id: 1, interestRate: .08, presentValue: 10000 },
   { _id: 2, interestRate: .0825, presentValue: 250000 },
   { _id: 3, interestRate: .0425, presentValue: 1000 }
] )

The following example calculates the effective interest rate for continuous compounding:

db.accounts.aggregate( [ { $project: { effectiveRate: { $subtract: [ { $exp: "$interestRate"}, 1 ] } } } ] )

The operation returns the following results:

{ "_id" : 1, "effectiveRate" : 0.08328706767495864 }
{ "_id" : 2, "effectiveRate" : 0.08599867343905654 }
{ "_id" : 3, "effectiveRate" : 0.04341605637367807 }