$isoWeekYear (aggregation)

Definition

$isoWeekYear

New in version 3.4.

Returns the year number in ISO 8601 format. The year starts with the Monday of week 1 and ends with the Sunday of the last week.

The $isoWeekYear expression has the following operator expression syntax:

{ $isoWeekYear: <dateExpression> }

The argument can be:

• An expression that resolves to a Date, a Timestamp, or an ObjectID.

• A document with this format:

  { date: <dateExpression>, timezone: <tzExpression> }
  Field	Description
  date	The date to which the operator is applied. <dateExpression> must be a valid expression that resolves to a Date, a Timestamp, or an ObjectID.
  timezone	Optional. The timezone of the operation result. <tzExpression> must be a valid expression that resolves to a string formatted as either an Olson Timezone Identifier or a UTC Offset. If no timezone is provided, the result is displayed in UTC. Format Examples Olson Timezone Identifier "America/New_York" "Europe/London" "GMT" UTC Offset +/-[hh]:[mm], e.g. "+04:45" +/-[hh][mm], e.g. "-0530" +/-[hh], e.g. "+03"

Behavior

{ $isoWeekYear: new Date("2015-05-26") }

{ $isoWeekYear: { date: new Date("Jan 7, 2003") } }

{ $isoWeekYear: ISODate("2017-01-02T00:00:00Z") }

{ $isoWeekYear: {
    date: ISODate("2017-01-02T00:00:00Z"),
    timezone: "-0500"
} }

{ $isoWeekYear: {
    date: new Date("April 08, 2024"),
    timezone: "America/Chicago"
} }

{ $isoWeekYear: "March 28, 1976" }

{ $isoWeekYear: Date("2016-01-01") }

{ $isoWeekYear: "2009-04-09" }

Example

A collection called anniversaries contains the following documents:

{ "_id" : 1, "date" : ISODate("2016-01-01T00:00:00Z") }
{ "_id" : 2, "date" : ISODate("2016-01-04T00:00:00Z") }
{ "_id" : 3, "date" : ISODate("2015-01-01T00:00:00Z") }
{ "_id" : 4, "date" : ISODate("2014-04-21T00:00:00Z") }

The following operation returns the year number in ISO 8601 format for each date field.

db.anniversaries.aggregate( [
  {
    $project: {
      yearNumber: { $isoWeekYear: "$date" }
    }
  }
] )

The operation returns the following results:

{ "_id" : 1, "yearNumber" : 2015 }
{ "_id" : 2, "yearNumber" : 2016 }
{ "_id" : 3, "yearNumber" : 2015 }
{ "_id" : 4, "yearNumber" : 2014 }