Merging arrays into one array in same field MongoDB

Question

I have a question on merging arrays into one array in same field, but they are in different objects. I hope you will understand what I wanted after looking at the code below.

 db.addresses.find().pretty()
{
        "_id" : ObjectId("62a72be40c7db0af0b79d721"),
        "rollingStockNumber" : "922698325786980137200129101715063039706000000",
        "addresses" : [
                "Raximova",
                "Raximova",
                "Raximova",
                "Nazarbek",
                "Oxunboboyeva",
        ],
        "__v" : 0
}
{
        "_id" : ObjectId("62a8727978c18925711d40f2"),
        "rollingStockNumber" : "922698012567076507200129101700057022060000000",
        "addresses" : [
                "Toshkent",
                "Chuqursoy",
                "Chuqursoy",
                "Chuqursoy",
                "Chuqursoy",
                "Chuqursoy",
                "Chuqursoy",
                "Toshkent",
        ],
        "__v" : 0
}
{
        "_id" : ObjectId("62a878d778c18925711d40f7"),
        "rollingStockNumber" : "922720020326980977200102111555058048630000000",
        "addresses" : [
                "Oxangaron",
                "Oxangaron",
                "Oxangaron",
                "Oxangaron",
                "Oxangaron",
                "Oxangaron",
                "Jaloir"
        ],
        "__v" : 0
}

I wanted to merge "addresses" arrays in one array called "allAddresses", used $group, $concat, but failed...

 "allAddresses" : [
                    "Raximova",
                    "Raximova",
                    "Raximova",
                    "Nazarbek",
                    "Oxunboboyeva",
                    "Toshkent",
                    "Chuqursoy",
                    "Chuqursoy",
                    "Chuqursoy",
                    "Chuqursoy",
                    "Chuqursoy",
                    "Chuqursoy",
                    "Toshkent",
                    "Oxangaron",
                    "Oxangaron",
                    "Oxangaron",
                    "Oxangaron",
                    "Oxangaron",
                    "Oxangaron",
                    "Jaloir"
            ]

How can I achieve that? Thanks in advance.

Yong Shun · Accepted Answer · 2022-06-14 12:26:25Z

4

$group - Group by null and add addresses into addresses array. It returns a nested array.
$project - With $reduce to flatten nested array.

db.collection.aggregate([
  {
    $group: {
      _id: null,
      addresses: {
        $push: "$addresses"
      }
    }
  },
  {
    $project: {
      allAddresses: {
        $reduce: {
          input: "$addresses",
          initialValue: [],
          in: {
            "$concatArrays": [
              "$$value",
              "$$this"
            ]
          }
        }
      }
    }
  }
])

Sample Mongo Playground

answered Jun 14, 2022 at 12:26

Yong Shun

54.5k6 gold badges38 silver badges66 bronze badges

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3 Comments

83hru2 Over a year ago

Thanks, it works. By the way, is it same syntax for Node.js? Can I use like "const allAddresses = Address.aggregate(..........." ?!

Yong Shun Over a year ago

Yes, you can use the above pipeline in Node.JS. const response = Address.aggregate(/* Pipeline */); const allAddresses = response[0]["allAddresses];.

83hru2 Over a year ago

Bro, it shows undefined...( How can solve??

reverie_ss · Accepted Answer · 2023-09-22 06:26:56Z

1

Easier approach:

Unwind the existing array
Append all the unwind objects

Here is the code:

db.collection.aggregate([
  {
    $unwind: {
       path: "$addresses",
       preserveNullAndEmptyArrays: false,
    },
  },
  {
    $group: {
      _id: null,
      allAddresses: {
        "$push": "$addresses"
      }
    }
  }
])

edited Sep 22, 2023 at 6:26

reverie_ss

2,70425 silver badges30 bronze badges

answered Jan 9, 2023 at 10:20

avinash

212 bronze badges

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