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MongoDB Aggregation Set Operator - $setIsSubset

MongoDB: $setIsSubset

The MongoDB $setIsSubset operators take exactly two argument expressions i.e. two sets and returns true when the first array is a subset of the second, including when the first array equals the second array, and false otherwise.

Syntax:

{ $setIsSubset: [ <expression1>, <expression2> ] }
  • The $setIsSubset operator can only performs set operation on arrays and treated as sets. If any duplicate value contains in an array, it ignores by $setIsSubset operator. The order of the elements in not important in this operation..
  • When a set contains a nested array element, the $setIsSubset 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: $setIsSubset

The following aggregation operation uses the $setIsSubset operator compares the array A and B to determine if the A array is a subset of the B array:

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

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

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

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