$log10 (aggregation)
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Definition
$log10
New in version 3.2.
Calculates the log base 10 of a number and returns the result as a double.
$log10
has the following syntax:{ $log10: <number> } The
<number>
expression can be any valid expression as long as it resolves to a non-negative number. For more information on expressions, see Expressions.$log10
is equivalent to$log: [ <number>, 10 ]
expression.
Behavior
If the argument resolves to a value of null
or refers to a field that is
missing, $log10
returns null
. If the argument resolves to
NaN
, $log10
returns NaN
.
Example | Results |
---|---|
{ $log10: 1 } | 0 |
{ $log10: 10 } | 1 |
{ $log10: 100 } | 2 |
{ $log10: 1000 } | 3 |
Example
Create a collection named samples
with the following documents:
db.samples.insertMany( [ { _id: 1, H3O: 0.0025 }, { _id: 2, H3O: 0.001 }, { _id: 3, H3O: 0.02 } ] )
The following example calculates the pH value of the samples:
db.samples.aggregate( [ { $project: { pH: { $multiply: [ -1, { $log10: "$H3O" } ] } } } ] )
The operation returns the following results:
{ "_id" : 1, "pH" : 2.6020599913279625 } { "_id" : 2, "pH" : 3 } { "_id" : 3, "pH" : 1.6989700043360187 }