$setEquals (expression operator)

Definition

$setEquals

Compares two or more arrays and returns true if they have the same distinct elements and false otherwise.

$setEquals has the following syntax:

{ $setEquals: [ <expression1>, <expression2>, ... ] }

The arguments can be any valid expression as long as they each resolve to an array. For more information on expressions, see Expressions.

Behavior

$setEquals performs set operation on arrays, treating arrays as sets. If an array contains duplicate entries, $setEquals ignores the duplicate entries. $setEquals ignores the order of the elements.

If a set contains a nested array element, $setEquals does not descend into the nested array but evaluates the array at top-level.

Example	Result	Notes
`{ $setEquals: [ [ "a", "c" ], [ "a", "b" ]] }`	`false`	The arrays do not contain the same elements.
`{ $setEquals: [ [ "a", "c" ], [ "a", "b", "c" ]] }`	`false`	The arrays do not contain the same elements.
`{ $setEquals: [ [ "a", "b", "a" ], [ "b", "a" ]] }`	`true`	Both arrays contain the same unique elements. When treated as sets, the first array is `[ "a", "b" ]` because duplicates are ignored.
`{ $setEquals: [ [ "a", "b" ], [ [ "a", "b" ] ]] }`	`false`	The elements in the arrays are not equal. The first array contains the strings `"a"` and `"b"`, while the second contains an array `[ "a", "b" ]`.
`{ $setEquals: [ [ ], [ "a", "b" ]] }`	`false`	The elements in the arrays are not equal. The first array is empty and the second array has two string elements.
`{ $setEquals: [ [ "a", "a" ], [ "a", "b" ]] }`	`false`	The arrays do not contain the same unique elements. The first array only contains `"a"`, while the second array contains `"a"` and `"b"`.

Example

Consider a bakeryOrders collection with the following documents:

db.bakeryOrders.insertMany( [   { _id: 0, cakes: ["chocolate", "vanilla"], cupcakes: ["chocolate", "vanilla"] },   { _id: 1, cakes: ["chocolate", "vanilla"], cupcakes: ["vanilla", "chocolate"] },   { _id: 2, cakes: ["chocolate", "chocolate"], cupcakes: ["chocolate"] },   { _id: 3, cakes: ["vanilla"], cupcakes: ["chocolate"] },   { _id: 4, cakes: ["vanilla"], cupcakes: [] }] )

The following operation uses the $setEquals operator to determine if the cakes array and the cupcakes array in each order contain the same flavors:

db.bakeryOrders.aggregate(   [      {         $project: {            _id: 0,            cakes: 1,            cupcakes: 1,            sameFlavors: { $setEquals: [ "$cakes", "$cupcakes" ] }         }      }   ] )

Note

$project

The $project stage specifies which fields are included in the output documents. In this example, the $project stage:

Excludes the _id field from the output.
Includes the cakes and cupcakes fields in the output.
Outputs the result of the $setEquals operator in a new field called sameFlavors.

The operation returns the following results:

{ cakes: [ "chocolate", "vanilla" ], cupcakes: [ "chocolate", "vanilla" ], sameFlavors: true},{ cakes: [ "chocolate", "vanilla" ], cupcakes: [ "vanilla", "chocolate" ], sameFlavors: true},{ cakes: [ "chocolate", "chocolate" ], cupcakes: [ "chocolate" ], sameFlavors: true},{ cakes: [ "vanilla" ], cupcakes: [ "chocolate" ], sameFlavors: false},{   cakes: [ "vanilla" ],   cupcakes: [],   sameFlavors: false}

Back

$setDifference

$setField