MongoDB Aggregation Set Operator - $setEquals

MongoDB: $setEquals

The MongoDB $setEquals operators compare between two or more arrays and returns true if they have the same distinct elements otherwise it returns false.

Syntax:

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

• The $setEquals operator in MongoDB performs set operation on arrays, the arrays provided in the operator retreated as sets. The duplicate entries in an array, ignore by the $setEquals operator. $setEquals ignores the order of the elements.
• If there is a nested array element in a set, the $setEquals operator does not descend into the nested array but evaluates the array at top-level.

Sample collection test_collection

{ "_id" : 1, "A" : [ "cat", "rat" ], "B" : [ "cat", "rat" ] }
{ "_id" : 2, "A" : [ "cat", "rat" ], "B" : [ ] }
{ "_id" : 3, "A" : [ ], "B" : [ "cat" ] }
{ "_id" : 4, "A" : [ "cat", "rat" ], "B" : [ "rat", "cat", "rat" ] }
{ "_id" : 5, "A" : [ "cat", "rat" ], "B" : [ "cat", "rat", "dog" ] }
{ "_id" : 6, "A" : [ "cat", "rat" ], "B" : [ [ "cat", "rat" ] ] }
{ "_id" : 7, "A" : [ "cat", "rat" ], "B" : [ [ "cat" ], [ "rat" ] ] }
{ "_id" : 8, "A" : [ ], "B" : [ ] }
{ "_id" : 9, "A" : [ "cat", "rat" ], "B" : [ "dog", "cat" ] }
}

Example: $setEquals

The following aggregation operation uses the $setEquals operator compares the array A and B to determine whether the arrays contain the same elements:

> db.test_collection.aggregate(
...    [
...      { $project: { A: 1, B: 1, sameElements: { $setEquals: [ "$A", "$B" ] }, _id: 0 } }
...    ]
... );

After the operation, following result will be returned by the $setEquals operator.

> db.test_collection.aggregate(
...    [
...      { $project: { A: 1, B: 1, sameElements: { $setEquals: [ "$A", "$B" ] }, _id: 0 } }
...    ]
... );
{ "A" : [ "cat", "rat" ], "B" : [ "cat", "rat" ], "sameElements" : true }
{ "A" : [ "cat", "rat" ], "B" : [ ], "sameElements" : false }
{ "A" : [ ], "B" : [ "cat" ], "sameElements" : false }
{ "A" : [ "cat", "rat" ], "B" : [ "rat", "cat", "rat" ], "sameElements" : true }
{ "A" : [ "cat", "rat" ], "B" : [ "cat", "rat", "dog" ], "sameElements" : false }
{ "A" : [ "cat", "rat" ], "B" : [ [ "cat", "rat" ] ], "sameElements" : false }
{ "A" : [ "cat", "rat" ], "B" : [ [ "cat" ], [ "rat" ] ], "sameElements" : false }
{ "A" : [ ], "B" : [ ], "sameElements" : true }
{ "A" : [ "cat", "rat" ], "B" : [ "dog", "cat" ], "sameElements" : false }

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