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$range (aggregation)

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Definition

$range

Returns an array whose elements are a generated sequence of numbers. $range generates the sequence from the specified starting number by successively incrementing the starting number by the specified step value up to but not including the end point.

$range has the following operator expression syntax:

{ $range: [ <start>, <end>, <non-zero step> ] }
Operand Description
<start> An integer that specifies the start of the sequence. Can be any valid expression that resolves to an integer.
<end> An integer that specifies the exclusive upper limit of the sequence. Can be any valid expression that resolves to an integer.
<non-zero step> Optional. An integer that specifies the increment value. Can be any valid expression that resolves to a non-zero integer. Defaults to 1.

Behavior

The <start> and <end> arguments are required and must be integers. The <non-zero step> argument is optional, and defaults to 1 if omitted.

Example Results
{ $range: [ 0, 10, 2 ] } [ 0, 2, 4, 6, 8 ]
{ $range: [ 10, 0, -2 ] } [ 10, 8, 6, 4, 2 ]
{ $range: [ 0, 10, -2 ] } [ ]
{ $range: [ 0, 5 ] } [ 1, 2, 3, 4, 5]

Example

The following example uses a collection called distances that lists cities along with their distance in miles from San Francisco.

Documents in the distances collection:

{ _id: 0, city: "San Jose", distance: 42 }
{ _id: 1, city: "Sacramento", distance: 88 }
{ _id: 2, city: "Reno", distance: 218 }
{ _id: 3, city: "Los Angeles", distance: 383 }

A bicyclist is planning to ride from San Francisco to each city listed in the collection and wants to stop and rest every 25 miles. The following aggregation pipeline operation uses the $range operator to determine the stopping points for each trip.

db.distances.aggregate([{
    $project: {
        _id: 0,
        city: 1,
        "Rest stops": { $range: [ 0, "$distance", 25 ] }
    }
}])

The operation returns the following:

{ "city" : "San Jose", "Rest stops" : [ 0, 25 ] }
{ "city" : "Sacramento", "Rest stops" : [ 0, 25, 50, 75 ] }
{ "city" : "Reno", "Rest stops" : [ 0, 25, 50, 75, 100, 125, 150, 175, 200 ] }
{ "city" : "Los Angeles", "Rest stops" : [ 0, 25, 50, 75, 100, 125, 150, 175, 200, 225, 250, 275, 300, 325, 350, 375 ] }