db.command.aggregate.abs

1. Operator Description

Function: Returns the absolute value of a numeric parameter.

Declaration: db.command.aggregate.abs(num)

2. Operator Parameters

Field	Type	Required	Description
-	Expression	Required	aggregate expression (must resolve to a number)

Notes:

If the expression resolves to null or points to a non-existent field, abs returns null. If the value resolves to NaN, it returns NaN.

3. Sample Code

Suppose the collection ratings contains the following records:

{ _id: 1, start: 5, end: 8 }
{ _id: 2, start: 4, end: 4 }
{ _id: 3, start: 9, end: 7 }
{ _id: 4, start: 6, end: 7 }

··· The absolute difference between start and end for each record can be calculated as follows:

// Sample code in the Cloud Function environment
const tcb = require('@cloudbase/node-sdk')
const app = tcb.init({
  env: 'xxx'
})

const db = app.database()
const $ = db.command.aggregate

exports.main = async (event, context) => {
  const res = await db
    .collection('ratings')
    .aggregate()
    .project({
      delta: $.abs($.subtract(['$start', '$end']))
    })
    .end()
  console.log(res.data)
}

The returned result is as follows:

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