# $ln (aggregation)¶

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## Definition¶

`$ln`

¶*New in version 3.2*.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 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 }

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