$setUnion (aggregation)

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Definition定义

$setUnion

Takes two or more arrays and returns an array containing the elements that appear in any input array.获取两个或多个数组并返回一个数组，该数组包含出现在任何输入数组中的元素。

$setUnion has the following syntax:语法如下所示：

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

The arguments can be any valid expression as long as they each resolve to an array. 参数可以是任何有效的表达式，只要它们各自解析为一个数组。For more information on expressions, see Expressions.有关表达式的详细信息，请参阅表达式。

Behavior行为

$setUnion performs set operation on arrays, treating arrays as sets. 对数组执行集合操作，将数组视为集合。If an array contains duplicate entries, $setUnion ignores the duplicate entries. 如果数组包含重复项，$setUnion将忽略重复项。$setUnion ignores the order of the elements.$setUnion忽略元素的顺序。

$setUnion filters out duplicates in its result to output an array that contain only unique entries. 筛选掉结果中的重复项，以输出只包含唯一项的数组。The order of the elements in the output array is unspecified.未指定输出数组中元素的顺序。

If a set contains a nested array element, $setUnion does not descend into the nested array but evaluates the array at top-level.如果集合包含嵌套数组元素，$setUnion不会下降到嵌套数组中，而是在顶级对数组求值。

Example示例Result
 
{ $setUnion: [ [ "a", "b", "a" ], [ "b", "a" ] ] }
 
[ "b", "a" ]
{ $setUnion: [ [ "a", "b" ], [ [ "a", "b" ] ] ] }
 
[ [ "a", "b" ], "b", "a" ]

Example示例

Consider an experiments collection with the following documents:考虑一个experiments集合带有下列文档：

{ "_id" : 1, "A" : [ "red", "blue" ], "B" : [ "red", "blue" ] }
{ "_id" : 2, "A" : [ "red", "blue" ], "B" : [ "blue", "red", "blue" ] }
{ "_id" : 3, "A" : [ "red", "blue" ], "B" : [ "red", "blue", "green" ] }
{ "_id" : 4, "A" : [ "red", "blue" ], "B" : [ "green", "red" ] }
{ "_id" : 5, "A" : [ "red", "blue" ], "B" : [ ] }
{ "_id" : 6, "A" : [ "red", "blue" ], "B" : [ [ "red" ], [ "blue" ] ] }
{ "_id" : 7, "A" : [ "red", "blue" ], "B" : [ [ "red", "blue" ] ] }
{ "_id" : 8, "A" : [ ], "B" : [ ] }
{ "_id" : 9, "A" : [ ], "B" : [ "red" ] }

The following operation uses the $setUnion operator to return an array of elements found in the A array or the B array or both:以下操作使用$setUnion运算符返回在A数组或B数组中找到的元素数组，或同时返回两者：

db.experiments.aggregate(
   [
     { $project: { A:1, B: 1, allValues: { $setUnion: [ "$A", "$B" ] }, _id: 0 } }
   ]
)

The operation returns the following results:操作返回以下结果：

{ "A": [ "red", "blue" ], "B": [ "red", "blue" ], "allValues": [ "blue", "red" ] }
{ "A": [ "red", "blue" ], "B": [ "blue", "red", "blue" ], "allValues": [ "blue", "red" ] }
{ "A": [ "red", "blue" ], "B": [ "red", "blue", "green" ], "allValues": [ "blue", "red", "green" ] }
{ "A": [ "red", "blue" ], "B": [ "green", "red" ], "allValues": [ "blue", "red", "green" ] }
{ "A": [ "red", "blue" ], "B": [ ], "allValues": [ "blue", "red" ] }
{ "A": [ "red", "blue" ], "B": [ [ "red" ], [ "blue" ] ], "allValues": [ "blue", "red", [ "red" ], [ "blue" ] ] }
{ "A": [ "red", "blue" ], "B": [ [ "red", "blue" ] ], "allValues": [ "blue", "red", [ "red", "blue" ] ] }
{ "A": [ ], "B": [ ], "allValues": [ ] }
{ "A": [ ], "B": [ "red" ], "allValues": [ "red" ] }