$cos (aggregation)
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Definition
$cos
Returns the cosine of a value that is measured in radians.
$cos
has the following syntax:{ $cos: <expression> } $cos
takes any valid expression that resolves to a number. If the expression returns a value in degrees, use the$degreesToRadians
operator to convert the result to radians.By default
$cos
returns values as adouble
.$cos
can also return values as a 128bit decimal as long as the<expression>
resolves to a 128bit decimal value.For more information on expressions, see Expression Operators.
Behavior
null
, NaN
, and +/ Infinity
If the argument resolves to a value of null
or refers to a field
that is missing, $cos
returns null
. If the
argument resolves to NaN
, $cos
returns NaN
.
If the argument resolves to negative or positive infinity,
$cos
throws an error.
Example  Results  

{ $cos: NaN }  NaN  
{ $cos: null }  null  
or
 Throws an error message resembling the following formatted output:

Example
The trigonometry
collection contains a document that
stores the hypotenuse and one angle in a rightangle triangle:
{ "_id" : ObjectId("5c50782193f833234ba90d85"), "angle_a" : NumberDecimal("53.13010235415597870314438744090659"), "hypotenuse" : NumberDecimal("5") }
The following aggregation operation uses the
$cos
expression to calculate the side adjacent
to angle_a
and add it to the input document using the
$addFields
pipeline stage.
db.trigonometry.aggregate([ { $addFields : { "side_a" : { $multiply : [ { $cos : {$degreesToRadians : "$angle_a"} }, "$hypotenuse" ] } } } ])
The $degreesToRadians
expression converts the
degree value of angle_a
to the equivalent value in radians.
The command returns the following output:
{ "_id" : ObjectId("5c50782193f833234ba90d85"), "angle_a" : NumberDecimal("53.13010235415597870314438744090659"), "side_a" : NumberDecimal("2.999999999999999999999999999999999"), "hypotenuse" : NumberDecimal("5"), }
Since angle_a
and hypotenuse
are stored as
128bit decimals, the output of
$cos
is a 128bit decimal.
The trigonometry
collection contains a document that
stores the hypotenuse and one angle in a rightangle triangle:
{ "_id" : ObjectId("5c50782193f833234ba90d85"), "angle_a" : NumberDecimal("0.9272952180016122324285124629224288"), "hypotenuse" : NumberDecimal("5") }
The following aggregation operation uses the
$cos
expression to calculate the side adjacent
to angle_a
and add it to the input document using the
$addFields
pipeline stage.
db.trigonometry.aggregate([ { $addFields : { "side_b" : { $multiply : [ { $cos : "$angle_a" }, "$hypotenuse" ] } } } ])
The command returns the following output:
{ "_id" : ObjectId("5c50782193f833234ba90d85"), "angle_a" : NumberDecimal("0.9272952180016122324285124629224288"), "side_b" : NumberDecimal("3.000000000000000000000000000000000"), "hypotenuse" : NumberDecimal("5"), }
Since angle_a
and hypotenuse
are stored as
128bit decimals, the output of
$cos
is a 128bit decimal.