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- $ln (aggregation)
$ln (aggregation)¶
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Definition¶
- $ln¶
3.2 新版功能.
Calculates the natural logarithm ln (i.e loge) 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 Expressions.
$ln is equivalent to $log: [ <number>, Math.E ] expression, where Math.E is a JavaScript representation for Euler’s number e.
Behavior¶
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 |
Example¶
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 }
参见