db.command.aggregate.log

1. Operator Description

Function: Computes the logarithm of a given number to a given base.

Syntax: db.command.aggregate.log([number, base])

2. Operator Parameters

Field	Type	Required	Description
-	<Array>Expression	Yes	<number> can be any expression that resolves to a non-negative number. <base> can be any expression that resolves to a number greater than 1.

Notes:

If any argument resolves to null or points to a missing field, log returns null. If any argument resolves to NaN, log returns NaN.

3. Sample Code

Suppose the collection staff contains the following records:

{ _id: 1, x: 1 }
{ _id: 2, x: 2 }
{ _id: 3, x: 3 }

Calculate the value of log2(x):

// 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('staff')
    .aggregate()
    .project({
      log: $.log(['$x', 2])
    })
    .end()
  console.log(res.data)
}

The returned result is as follows:

{ _id: 1, log: 0 }
{ _id: 2, log: 1 }
{ _id: 3, log: 1.58496250072 }