Merge array elements and dedup Mongodb aggregate

Question

I have below two document on the collection. I need the output grouped by manager level with the list of items assigned under his team.

Input

{ 
            "emp" : "emp1", 
            "itemList" : [
                "item1", 
                "item2", 
                "item3", 
                "item4"
            ], 
            "reportingTo" : "manager1"
        }
        { 
            "emp" : "emp2", 
            "itemList" : [
                "item5", 
                "item2", 
                "item3", 
                "item4"
            ], 
            "reportingTo" : "manager1"
        }

output:

    {
    "reportingTo":"manager1",
        "itemList" : [
            "item1", 
            "item2", 
            "item3", 
            "item4",
            "item5"
        ]
    }

Ashh · Accepted Answer · 2019-11-18 10:29:15Z

1

You can use below aggregation

db.collection.aggregate([
  { "$group": {
    "_id": "$reportingTo",
    "itemList": {
      "$addToSet": "$itemList"
    }
  }},
  { "$project": {
    "reportingTo": "$_id",
    "itemList": {
      "$reduce": {
        "input": "$itemList",
        "initialValue": [],
        "in": { "$setUnion": ["$$this", "$$value"] }
      }
    }
  }}
])

answered Nov 18, 2019 at 10:29

Ashh

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