$setUnion (aggregation)
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Definition
$setUnion
Takes two or more arrays and returns an array containing the elements that appear in any input array.
$setUnion
has the following syntax:{ $setUnion: [ <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
$setUnion
performs set operation on arrays, treating arrays
as sets. If an array contains duplicate entries, $setUnion
ignores the duplicate entries. $setUnion
ignores the order of
the elements.
$setUnion
filters out duplicates in its result to output an
array that contain only unique entries. The order of the elements in
the output array is unspecified.
If a set contains a nested array element, $setUnion
does not descend
into the nested array but evaluates the array at top-level.
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Example
Consider an flowers
collection with the following documents:
db.flowers.insertMany( [ { "_id" : 1, "flowerFieldA" : [ "rose", "orchid" ], "flowerFieldB" : [ "rose", "orchid" ] }, { "_id" : 2, "flowerFieldA" : [ "rose", "orchid" ], "flowerFieldB" : [ "orchid", "rose", "orchid" ] }, { "_id" : 3, "flowerFieldA" : [ "rose", "orchid" ], "flowerFieldB" : [ "rose", "orchid", "jasmine" ] }, { "_id" : 4, "flowerFieldA" : [ "rose", "orchid" ], "flowerFieldB" : [ "jasmine", "rose" ] }, { "_id" : 5, "flowerFieldA" : [ "rose", "orchid" ], "flowerFieldB" : [ ] }, { "_id" : 6, "flowerFieldA" : [ "rose", "orchid" ], "flowerFieldB" : [ [ "rose" ], [ "orchid" ] ] }, { "_id" : 7, "flowerFieldA" : [ "rose", "orchid" ], "flowerFieldB" : [ [ "rose", "orchid" ] ] }, { "_id" : 8, "flowerFieldA" : [ ], "flowerFieldB" : [ ] }, { "_id" : 9, "flowerFieldA" : [ ], "flowerFieldB" : [ "rose" ] } ] )
The following operation uses the $setUnion
operator to
return an array of elements found in the flowerFieldA
array or the
flowerFieldB
array or both:
db.flowers.aggregate( [ { $project: { flowerFieldA:1, flowerFieldB: 1, allValues: { $setUnion: [ "$flowerFieldA", "$flowerFieldB" ] }, _id: 0 } } ] )
The operation returns the following results:
{ "flowerFieldA": [ "rose", "orchid" ], "flowerFieldB": [ "rose", "orchid" ], "allValues": [ "orchid", "rose" ] } { "flowerFieldA": [ "rose", "orchid" ], "flowerFieldB": [ "orchid", "rose", "orchid" ], "allValues": [ "orchid", "rose" ] } { "flowerFieldA": [ "rose", "orchid" ], "flowerFieldB": [ "rose", "orchid", "jasmine" ], "allValues": [ "orchid", "rose", "jasmine" ] } { "flowerFieldA": [ "rose", "orchid" ], "flowerFieldB": [ "jasmine", "rose" ], "allValues": [ "orchid", "rose", "jasmine" ] } { "flowerFieldA": [ "rose", "orchid" ], "flowerFieldB": [ ], "allValues": [ "orchid", "rose" ] } { "flowerFieldA": [ "rose", "orchid" ], "flowerFieldB": [ [ "rose" ], [ "orchid" ] ], "allValues": [ "orchid", "rose", [ "rose" ], [ "orchid" ] ] } { "flowerFieldA": [ "rose", "orchid" ], "flowerFieldB": [ [ "rose", "orchid" ] ], "allValues": [ "orchid", "rose", [ "rose", "orchid" ] ] } { "flowerFieldA": [ ], "flowerFieldB": [ ], "allValues": [ ] } { "flowerFieldA": [ ], "flowerFieldB": [ "rose" ], "allValues": [ "rose" ] }