如何在MongoDB中的单个集合中找到文档之间的集合的交集? [英] How to find set intersection of sets between the documents in a single collection in MongoDB?

问题描述

下面的名为"coll"的集合在mongodb中维护.

The below collection named "coll" was maintained in the mongodb.

{
    {"_id":1, "set":[1,2,3,4,5]},
    {"_id":2, "set":[0,2,6,4,5]},
    {"_id":3, "set":[1,2,5,10,22]}
}

如何在上述收集文档中找到集合元素与_id的1和3的交集.

How to find the intersection of the set elements in the above collection documents with _id's 1 and 3.

推荐答案

使用 设置运算符 魔术是 $setIntersection .

以下聚合管道可以实现您所追求的目标:

The following aggregation pipeline achieves what you are after:

db.test.aggregate([
    {
        "$match": {
            "_id": { "$in": [1, 3] }
        }
    },
    {
        "$group": {
            "_id": 0,
            "set1": { "$first": "$set" },
            "set2": { "$last": "$set" }
        }
    },
    {
        "$project": { 
            "set1": 1, 
            "set2": 1, 
            "commonToBoth": { "$setIntersection": [ "$set1", "$set2" ] }, 
            "_id": 0 
        }
    }
])

输出:

/* 0 */
{
    "result" : [ 
        {
            "set1" : [1,2,3,4,5],
            "set2" : [1,2,5,10,22],
            "commonToBoth" : [1,2,5]
        }
    ],
    "ok" : 1
}

---

更新

要相交三个或更多文档，您需要 $reduce 运算符以展平数组.这将使您可以与任意数量的数组相交，因此，这不仅适用于文档1和3中两个数组的相交，而且还适用于多个数组.

---

UPDATE

For three or more documents to be intersected, you'd need the $reduce operator to flatten the arrays. This will allow you to intersect any number of arrays, so instead of just doing an intersection of the two arrays from docs 1 and 3, this will apply to multiple arrays as well.

考虑运行以下聚合操作:

Consider running the following aggregate operation:

db.test.aggregate([
    { "$match": { "_id": { "$in": [1, 3] } } },
    {
        "$group": {
            "_id": 0,
            "sets": { "$push": "$set" },
            "initialSet": { "$first": "$set" }
        }
    },
    {
        "$project": {
            "commonSets": {
                "$reduce": {
                    "input": "$sets",
                    "initialValue": "$initialSet",
                    "in": { "$setIntersection": ["$$value", "$$this"] }
                }
            }
        }
    }
])

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