$cos (aggregation)

Definition

  • $cos

New in version 4.2.

Returns the cosine of a value that is measured in radians.

$cos has the following syntax:

  1. { $cos: <expression> }

$cos takes any valid expression that resolves to a number. If theexpression returns a value in degrees, use the$degreesToRadians operator to convert theresult to radians.

By default $cos returns values as a double.$cos can also return values as a128-bit decimalas long as the <expression> resolves to a 128-bit decimal value.

For more information on expressions, seeExpressions.

Behavior

null, NaN, and +/- Infinity

If the argument resolves to a value of null or refers to a fieldthat is missing, $cos returns null. If theargument resolves to NaN, $cos returns NaN.If the argument resolves to negative or positive infinity,$cos throws an error.

ExampleResults
{ $cos: NaN }NaN
{ $cos: null }null
{ $cos : Infinity}or{ $cos : -Infinity }Throws an error message resembling the following formattedoutput:
  1. "errmsg" :  "Failed to optimize pipeline :: caused by :: cannot  apply $cos to -inf, value must in (-inf,inf)"

Example

  • Cosine of Value in Degrees
  • Sine of Value in Radians

The trigonometry collection contains a document thatstores the hypotenuse and one angle in a right-angle triangle:

  1. {
  2.   "_id" : ObjectId("5c50782193f833234ba90d85"),
  3.   "angle_a" : NumberDecimal("53.13010235415597870314438744090659"),
  4.   "hypotenuse" : NumberDecimal("5")
  5. }

The following aggregation operation uses the$cos expression to calculate the side adjacentto angle_a and add it to the input document using the$addFields pipeline stage.

  1. db.trigonometry.aggregate([
  2.   {
  3.     $addFields : {
  4.       "side_a" : {
  5.         $multiply : [
  6.           { $cos : {$degreesToRadians : "$angle_a"} },
  7.           "$hypotenuse"
  8.         ]
  9.       }
  10.     }
  11.   }
  12. ])

The $degreesToRadians expression converts thedegree value of angle_a to the equivalent value in radians.

The command returns the following output:

  1. {
  2.   "_id" : ObjectId("5c50782193f833234ba90d85"),
  3.   "angle_a" : NumberDecimal("53.13010235415597870314438744090659"),
  4.   "side_a" : NumberDecimal("2.999999999999999999999999999999999"),
  5.   "hypotenuse" : NumberDecimal("5"),
  6. }

Since angle_a and hypotenuse are stored as128-bit decimals, the output of$cos is a 128-bit decimal.

The trigonometry collection contains a document thatstores the hypotenuse and one angle in a right-angle triangle:

  1. {
  2.   "_id" : ObjectId("5c50782193f833234ba90d85"),
  3.   "angle_a" : NumberDecimal("0.9272952180016122324285124629224288"),
  4.   "hypotenuse" : NumberDecimal("5")
  5. }

The following aggregation operation uses the$cos expression to calculate the side adjacentto angle_a and add it to the input document using the$addFields pipeline stage.

  1. db.trigonometry.aggregate([
  2.   {
  3.     $addFields : {
  4.       "side_b" : {
  5.         $multiply : [
  6.           { $cos : "$angle_a" },
  7.           "$hypotenuse"
  8.         ]
  9.       }
  10.     }
  11.   }
  12. ])

The command returns the following output:

  1. {
  2.   "_id" : ObjectId("5c50782193f833234ba90d85"),
  3.   "angle_a" : NumberDecimal("0.9272952180016122324285124629224288"),
  4.   "side_b" : NumberDecimal("3.000000000000000000000000000000000"),
  5.   "hypotenuse" : NumberDecimal("5"),
  6. }

Since angle_a and hypotenuse are stored as128-bit decimals, the output of$cos is a 128-bit decimal.