在没有$ unwind的情况下在数组中查找重复项

问题描述

我有以下用户收藏

[{
    "_id": 1,
    "adds": ["111", "222", "333", "111"]
}, {
    "_id": 2,
    "adds": ["555", "666", "777", "555"]
}, {
    "_id": 3,
    "adds": ["888", "999", "000", "888"]
}]

我需要在adds数组中找到重复项

I need to find the duplicates inside the adds array

预期输出应为

[{
    "_id": 1,
    "adds": ["111"]
}, {
    "_id": 2,
    "adds": [ "555"]
}, {
    "_id": 3,
    "adds": ["888"]
}]

我尝试使用许多运算符$setUnion，$setDifference，但是没有一个成功.

I have tried using many operators $setUnion, $setDifference but none of the did the trick.

请帮助！

推荐答案

您可以使用 $ range 生成从1到n的数字数组，其中n是adds的rel =" nofollow noreferrer> $ size .然后，您可以循环"通过这些数字，并检查index处的adds( $ arrayElemAt )在index之前的某个位置存在(如果是)，则应将其视为重复项.您可以使用 $ indexOfArray 检查元素是否存在在数组中指定0和index作为搜索范围.

You can use $range to generate arrays of numbers from 1 to n where n is the $size of adds. Then you can "loop" through that numbers and check if adds at index ($arrayElemAt) exists somewhere before index if yes then it should be considered as a duplicate. You can use $indexOfArray to check if element exists in array specifying 0 and index as search range.

然后，您只需要使用$project和 $映射以将索引替换为实际元素.您还可以添加 $ setUnion 以避免重复的重复在最终结果集中.

Then you just need to use $project and $map to replace indexes with actual elements. You can also add $setUnion to avoid duplicated duplicates in final result set.

db.users.aggregate([
    {
        $addFields: {
            duplicates: {
                $filter: {
                    input: { $range: [ 1, { $size: "$adds" } ] },
                    as: "index",
                    cond: {
                        $ne: [ { $indexOfArray: [ "$adds", { $arrayElemAt: [ "$adds", "$$index" ]  }, 0, "$$index" ] }, -1 ]
                    }
                }
            }
        }
    },
    {
        $project: {
            _id: 1,
            adds: {
                $setUnion: [ { $map: { input: "$duplicates", as: "d", in: { $arrayElemAt: [ "$adds", "$$d" ] } } }, [] ]
            }
        }
    }
])

打印:

{ "_id" : 1, "adds" : [ "111" ] }
{ "_id" : 2, "adds" : [ "555" ] }
{ "_id" : 3, "adds" : [ "888" ] }

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