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$acos (aggregation)

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$acos

New in version 4.2.

Returns the inverse cosine (arc cosine) of a value.

$acos has the following syntax:

{ $acos: <expression> }

$acos takes any valid expression that resolves to a number between -1 and 1, e.g. -1 <= value <= 1.

$acos returns values in radians. Use $radiansToDegrees operator to convert the output value from radians to degrees.

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

For more information on expressions, see Expressions.

Behavior

If the argument resolves to a value of null or refers to a field that is missing, $acos returns null. If the argument resolves to NaN, $acos returns NaN. If the argument resolves to a value outside the bounds of [-1, 1] inclusive, $acos throws an error.

ExampleResults
{ $acos: NaN }NaN
{ $acos: null }null
{ $acos : Infinity}
or
{ $acos : -Infinity } 		Throws an error message resembling the following formatted output: 
"errmsg" :
  "Failed to optimize pipeline :: caused by :: cannot
  apply $acos to -inf, value must in [-1,1]"

Example