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$abs (aggregation)

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  • Definition
  • Behavior
  • Example
$abs

Returns the absolute value of a number.

$abs has the following syntax:

{ $abs: <number> }

The <number> expression can be any valid expression as long as it resolves to a number. For more information on expressions, see Expressions.

If the argument resolves to a value of null or refers to a field that is missing, $abs returns null. If the argument resolves to NaN, $abs returns NaN.

Example
Results
{ $abs: -1 }
1
{ $abs: 1 }
1
{ $abs: null }
null

A collection temperatureChange contains the following documents:

db.temperatureChange.insertMany( [
{ _id: 1, startTemp: 50, endTemp: 80 },
{ _id: 2, startTemp: 40, endTemp: 40 },
{ _id: 3, startTemp: 90, endTemp: 70 },
{ _id: 4, startTemp: 60, endTemp: 70 }
] )

The following example calculates the magnitude of difference between the startTemp and endTemp ratings:

db.temperatureChange.aggregate([
{
$project: { delta: { $abs: { $subtract: [ "$startTemp", "$endTemp" ] } } }
}
])

The operation returns the following results:

{ "_id" : 1, "delta" : 30 }
{ "_id" : 2, "delta" : 0 }
{ "_id" : 3, "delta" : 20 }
{ "_id" : 4, "delta" : 10 }
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