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- $exp (aggregation)
$exp (aggregation)¶
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Definition¶
- $exp¶
3.2 新版功能.
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 Expressions.
Behavior¶
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 | Results |
|---|---|
| { $exp: 0 } | 1 |
| { $exp: 2 } | 7.38905609893065 |
| { $exp: -2 } | 0.1353352832366127 |
Example¶
A collection named accounts contains the following documents:
{ _id: 1, rate: .08, pv: 10000 }
{ _id: 2, rate: .0825, pv: 250000 }
{ _id: 3, rate: .0425, pv: 1000 }
The following example calculates the effective interest rate for continuous compounding:
db.accounts.aggregate( [ { $project: { effectiveRate: { $subtract: [ { $exp: "$rate"}, 1 ] } } } ] )
The operation returns the following results:
{ "_id" : 1, "effectiveRate" : 0.08328706767495864 }
{ "_id" : 2, "effectiveRate" : 0.08599867343905654 }
{ "_id" : 3, "effectiveRate" : 0.04341605637367807 }