$sqrt (aggregation)
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Definition
$sqrt
New in version 3.2.
Calculates the square root of a positive number and returns the result as a double.
$sqrt
has the following syntax:{ $sqrt: <number> } The argument can be any valid expression as long as it resolves to a non-negative number. 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, $sqrt
returns null
. If the argument resolves to
NaN
, $sqrt
returns NaN
.
$sqrt
errors on negative numbers.
Example | Results |
---|---|
{ $sqrt: 25 } | 5 |
{ $sqrt: 30 } | 5.477225575051661 |
{ $sqrt: null } | null |
Example
A collection points
contains the following documents:
{ _id: 1, p1: { x: 5, y: 8 }, p2: { x: 0, y: 5} } { _id: 2, p1: { x: -2, y: 1 }, p2: { x: 1, y: 5} } { _id: 3, p1: { x: 4, y: 4 }, p2: { x: 4, y: 0} }
The following example uses $sqrt
to calculate the
distance between p1
and p2
:
db.points.aggregate([ { $project: { distance: { $sqrt: { $add: [ { $pow: [ { $subtract: [ "$p2.y", "$p1.y" ] }, 2 ] }, { $pow: [ { $subtract: [ "$p2.x", "$p1.x" ] }, 2 ] } ] } } } } ])
The operation returns the following results:
{ "_id" : 1, "distance" : 5.830951894845301 } { "_id" : 2, "distance" : 5 } { "_id" : 3, "distance" : 4 }