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$week (aggregation)

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Definition

$week

Returns the week of the year for a date as a number between 0 and 53.

Weeks begin on Sundays, and week 1 begins with the first Sunday of the year. Days preceding the first Sunday of the year are in week 0. This behavior is the same as the “%U” operator to the strftime standard library function.

The $week expression has the following operator expression syntax:

{ $week: <dateExpression> }

Changed in version 3.6.

The argument must be a valid expression that resolves to one of the following:

  • A Date, a Timestamp, or an ObjectID.

  • A document of the following form:

    New in version 3.6.

    { 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

Example Result
{ $week: new Date("Jan 1, 2016") }
0
{ $week: { date: new Date("2016-01-04") } }
1
{ $week: {
    date: new Date("August 14, 2011"),
    timezone: "America/Chicago"
} }
33
{ $week: ISODate("1998-11-01T00:00:00Z") }
44
{ $week: {
    date: ISODate("1998-11-01T00:00:00Z"),
    timezone: "-0500"
} }
43
{ $week: "March 28, 1976" }
error
{ $week: Date("2016-01-01") }
error
{ $week: "2009-04-09" }
error

Note

$week cannot take a string as an argument.

Example

Consider a sales collection with the following document:

{
  "_id" : 1,
  "item" : "abc",
  "price" : 10,
  "quantity" : 2,
  "date" : ISODate("2014-01-01T08:15:39.736Z")
}

The following aggregation uses the $week and other date operators to break down the date field:

db.sales.aggregate(
   [
     {
       $project:
         {
           year: { $year: "$date" },
           month: { $month: "$date" },
           day: { $dayOfMonth: "$date" },
           hour: { $hour: "$date" },
           minutes: { $minute: "$date" },
           seconds: { $second: "$date" },
           milliseconds: { $millisecond: "$date" },
           dayOfYear: { $dayOfYear: "$date" },
           dayOfWeek: { $dayOfWeek: "$date" },
           week: { $week: "$date" }
         }
     }
   ]
)

The operation returns the following result:

{
  "_id" : 1,
  "year" : 2014,
  "month" : 1,
  "day" : 1,
  "hour" : 8,
  "minutes" : 15,
  "seconds" : 39,
  "milliseconds" : 736,
  "dayOfYear" : 1,
  "dayOfWeek" : 4,
  "week" : 0
}