In MongoDB, the $size aggregation pipeline operator counts and returns the total number of items in an array.

The $size operator accepts one argument. The argument can be any valid expression that resolves to an array.

In MongoDB, the $setUnion aggregation pipeline operator accepts two or more arrays and returns an array containing the elements that appear in any of those input arrays.

$setUnion accepts two or more arguments, all of which can be any valid expression as long as they each resolve to an array. $setUnion treats the arrays as sets.

In MongoDB, the $setIsSubset aggregation pipeline operator accepts two arrays and returns true when the first array is a subset of the second, and false when it isn’t.

The first array is also considered a subset when it equals the second array.

In MongoDB, the $setIntersection aggregation pipeline operator accepts two or more arrays and returns an array that contains the elements that appear in all input arrays.

$setIntersection accepts two or more arguments, all of which can be any valid expression as long as they each resolve to an array. $setIntersection treats the arrays as sets.

In MongoDB, the $setEquals aggregation pipeline operator compares two or more arrays and returns true if they have the same distinct elements and false otherwise.

$setEquals accepts two or more arguments, all of which can be any valid expression as long as they each resolve to an array. $setEquals treats the arrays as sets.

In MongoDB, the $setDifference aggregation pipeline operator accepts two sets and performs a relative complement of the second set relative to the first. It returns an array containing the elements that only exist in the first set.

$setDifference accepts two arguments, both of which can be any valid expression as long as they each resolve to an array. $setDifference treats the arrays as sets.