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(DOCSP-26896): Fix highlighting and formatting on $map (#2230)
* (DOCSP-26896): Fix highlighting and formatting on map * update TOC depth * fix example titles * standardize formatting * more formatting improvements * edits * alphabetize learn more
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‎source/reference/operator/aggregation/map.txt

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@@ -7,7 +7,7 @@ $map (aggregation)
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.. contents:: On this page
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:local:
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:backlinks: none
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:depth: 1
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:depth: 2
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:class: singlecol
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Definition
@@ -56,111 +56,149 @@ Definition
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Examples
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--------
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Add to each element of an array using ``$map``
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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Add to Each Element of an Array
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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From the :binary:`~bin.mongo` shell, create a sample collection named
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``grades`` with the following documents:
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.. code-block:: javascript
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db.grades.insertMany([
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{ _id: 1, quizzes: [ 5, 6, 7 ] },
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{ _id: 2, quizzes: [ ] },
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{ _id: 3, quizzes: [ 3, 8, 9 ] }
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])
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db.grades.insertMany( [
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{ quizzes: [ 5, 6, 7 ] },
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{ quizzes: [ ] },
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{ quizzes: [ 3, 8, 9 ] }
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] )
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The following aggregation operation uses :expression:`$map` with the
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:expression:`$add` expression to increment each element in the
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``quizzes`` array by ``2``.
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.. code-block:: javascript
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db.grades.aggregate(
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[
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{ $project:
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{ adjustedGrades:
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{
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$map:
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{
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input: "$quizzes",
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as: "grade",
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in: { $add: [ "$$grade", 2 ] }
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}
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}
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db.grades.aggregate( [
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{
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$project: {
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adjustedGrades: {
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$map: {
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input: "$quizzes",
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as: "grade",
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in: { $add: [ "$$grade", 2 ] }
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}
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}
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}
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]
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)
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}
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] )
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This operation returns the following results:
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.. code-block:: javascript
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:copyable: false
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{ "_id" : 1, "adjustedGrades" : [ 7, 8, 9 ] }
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{ "_id" : 2, "adjustedGrades" : [ ] }
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{ "_id" : 3, "adjustedGrades" : [ 5, 10, 11 ] }
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Truncate each array element with ``$map``
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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[
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{
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_id: ObjectId("6390b8f7237da390c6869a62"),
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adjustedGrades: [ 7, 8, 9 ]
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},
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{
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_id: ObjectId("6390b8f7237da390c6869a63"),
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adjustedGrades: []
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},
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{
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_id: ObjectId("6390b8f7237da390c6869a64"),
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adjustedGrades: [ 5, 10, 11 ]
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}
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]
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Truncate Each Array Element
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~~~~~~~~~~~~~~~~~~~~~~~~~~~
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From the :binary:`~bin.mongo` shell, create a sample collection named
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``deliveries`` with the following documents:
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.. code-block:: javascript
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db.deliveries.insertMany([
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{ "_id" : 1, "city" : "Bakersfield", "distances" : [ 34.57, 81.96, 44.24 ] },
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{ "_id" : 2, "city" : "Barstow", "distances" : [ 73.28, 9.67, 124.36 ] },
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{ "_id" : 3, "city" : "San Bernadino", "distances" : [ 16.04, 3.25, 6.82 ] }
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])
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db.deliveries.insertMany( [
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{
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"city" : "Bakersfield",
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"distances" : [ 34.57, 81.96, 44.24 ]
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},
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{
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"city" : "Barstow",
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"distances" : [ 73.28, 9.67, 124.36 ]
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},
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{
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"city" : "San Bernadino",
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"distances" : [ 16.04, 3.25, 6.82 ]
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}
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] )
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The following aggregation operation uses :expression:`$map` to
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:expression:`truncate <$trunc>` each element in the ``distances`` array
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to its integer.
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.. code-block:: javascript
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db.deliveries.aggregate(
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[
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{ $project:
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{ city: "$city",
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integerValues:
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{ $map:
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{
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input: "$distances",
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as: "decimalValue",
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in: { $trunc: "$$decimalValue" }
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}
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db.deliveries.aggregate( [
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{
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$project: {
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city: "$city",
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integerValues: {
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$map: {
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input: "$distances",
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as: "decimalValue",
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in: { $trunc: "$$decimalValue" }
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}
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}
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}
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]
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)
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}
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] )
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This operation returns the following results:
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.. code-block:: javascript
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:copyable: false
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{ "_id" : 1, "city" : "Bakersfield", "integerValues" : [ 34, 81, 44 ] }
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{ "_id" : 2, "city" : "Barstow", "integerValues" : [ 73, 9, 124 ] }
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{ "_id" : 3, "city" : "San Bernadino", "integerValues" : [ 16, 3, 6 ] }
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151-
Convert Celsius Temperatures to Fahrenheit Using ``$map``
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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[
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{
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_id: ObjectId("6390b9b1237da390c6869a65"),
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city: 'Bakersfield',
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integerValues: [ 34, 81, 44 ]
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},
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{
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_id: ObjectId("6390b9b1237da390c6869a66"),
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city: 'Barstow',
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integerValues: [ 73, 9, 124 ]
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},
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{
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_id: ObjectId("6390b9b1237da390c6869a67"),
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city: 'San Bernadino',
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integerValues: [ 16, 3, 6 ]
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}
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]
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Convert Celsius Temperatures to Fahrenheit
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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From the :binary:`~bin.mongo` shell, create a sample collection named
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``temperatures`` with the following documents:
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.. code-block:: javascript
158187

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db.temperatures.insertMany([
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{ "_id" : 1, "date" : ISODate("2019-06-23"), "tempsC" : [ 4, 12, 17 ] },
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{ "_id" : 2, "date" : ISODate("2019-07-07"), "tempsC" : [ 14, 24, 11 ] },
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{ "_id" : 3, "date" : ISODate("2019-10-30"), "tempsC" : [ 18, 6, 8 ] }
163-
])
188+
db.temperatures.insertMany( [
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{
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"date" : ISODate("2019-06-23"),
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"tempsC" : [ 4, 12, 17 ]
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},
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{
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"date" : ISODate("2019-07-07"),
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"tempsC" : [ 14, 24, 11 ]
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},
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{
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"date" : ISODate("2019-10-30"),
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"tempsC" : [ 18, 6, 8 ]
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}
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] )
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The following aggregation operation uses the :pipeline:`$addFields`
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stage to add a new field to the documents called ``tempsF`` which
@@ -172,17 +210,18 @@ values by ``9/5`` and then :expression:`$add` ``32``.
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.. code-block:: javascript
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db.temperatures.aggregate( [
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{ $addFields:
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{
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"tempsF":
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{ $map:
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{
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input: "$tempsC",
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as: "tempInCelsius",
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in: { $add: [ { $multiply: [ "$$tempInCelsius", 9/5 ] }, 32 ] }
213+
{
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$addFields: {
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"tempsF": {
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$map: {
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input: "$tempsC",
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as: "tempInCelsius",
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in: {
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$add: [ { $multiply: [ "$$tempInCelsius", 9/5 ] }, 32 ]
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}
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}
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}
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}
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}
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}
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] )
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@@ -191,12 +230,32 @@ This operation returns the following results:
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.. code-block:: javascript
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:copyable: false
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{ "_id" : 1, "date" : ISODate("2019-06-23T00:00:00Z"), "tempsC : [ 4, 12, 17 ], "tempsF" : [ 39.2, 53.6, 62.6 ] }
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{ "_id" : 2, "date" : ISODate("2019-07-07T00:00:00Z"), "tempsC" : [ 14, 24, 11 ], "tempsF" : [ 57.2, 75.2, 51.8 ] }
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{ "_id" : 3, "date" : ISODate("2019-10-30T00:00:00Z"), "tempsC" : [ 18, 6, 8 ], "tempsF" : [ 64.4, 42.8, 46.4 ] }
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[
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{
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_id: ObjectId("6390ba11237da390c6869a68"),
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date: ISODate("2019-06-23T00:00:00.000Z"),
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tempsC: [ 4, 12, 17 ],
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tempsF: [ 39.2, 53.6, 62.6 ]
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},
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{
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_id: ObjectId("6390ba11237da390c6869a69"),
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date: ISODate("2019-07-07T00:00:00.000Z"),
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tempsC: [ 14, 24, 11 ],
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tempsF: [ 57.2, 75.2, 51.8 ]
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},
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{
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_id: ObjectId("6390ba11237da390c6869a6a"),
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date: ISODate("2019-10-30T00:00:00.000Z"),
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tempsC: [ 18, 6, 8 ],
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tempsF: [ 64.4, 42.8, 46.4 ]
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}
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]
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Learn More
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----------
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.. seealso::
257+
To learn more about expressions used in the previous examples, see:
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200-
- :expression:`$let`
201-
- :expression:`$add`
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- :expression:`$multiply`
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- :expression:`$add`
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- :expression:`$let`
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- :expression:`$multiply`

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