Convert multiple array into one array in MongoDB, also remove the None values from Arrays

Question

Mongo DB Array Structure:

{

    "time" :[
           [2018-12-18T20:16:28.800Z , 2018-12-18T20:16:28.800Z, 2016-11-14T10:16:32.700Z],
           [2016-11-14T10:16:32.700Z, 2017-09-17T11:16:54.500Z, 2018-12-18T20:16:28.800Z],
           [2017-09-17T11:16:54.500Z, 2018-12-18T20:16:28.800Z, 2016-11-14T10:16:32.700Z]
],
    "bar": [
           [2,5,9,8],
           [6,3,7,None],
           [7,8,None]
    ]
}

Expected output with One array without None values:

"time" :[
2018-12-18T20:16:28.800Z, 
2018-12-18T20:16:28.800Z, 
2016-11-14T10:16:32.700Z,
2016-11-14T10:16:32.700Z, 
2017-09-17T11:16:54.500Z, 
2017-09-17T11:16:54.500Z, 
2016-11-14T10:16:32.700Z
],
    "bar": [
           2,
           5,
           9,
           6,
           3,
           7,
           8
]
}

I'm using Mongodb 4.2, and want to convert multiple arrays to one array, without $unwind. Because its reduce the performance in my case.

turivishal · Accepted Answer · 2020-11-09 09:17:00Z

1

You can try,

time, $reduce to iterate loop of time and $concatArrays to merge the arrays
bar, $reduce to iterate loop of bar and $concatArrays to merge the arrays and get unique value, $filter to iterate loop of updated array from $reduce and remove None value from that array

db.collection.aggregate([
  {
    $project: {
      time: {
        $reduce: {
          input: "$time",
          initialValue: [],
          in: { $concatArrays: ["$$value", "$$this"] }
        }
      },
      bar: {
        $filter: {
          input: {
            $reduce: {
              input: "$bar",
              initialValue: [],
              in: { $concatArrays: ["$$value", "$$this"] }
            }
          },
          cond: { $ne: ["$$this", "None"] }
        }
      }
    }
  }
])

Playground

edited Nov 9, 2020 at 9:17

answered Nov 9, 2020 at 8:37

turivishal

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7 Comments

bc110402922 Over a year ago

Thanks for the answer, but after this condition, I'm not getting repeated values, bar contains the multiple repeated values inside the array. just want to exclude the "None"

turivishal Over a year ago

Okay got it i looked at your expected that was unique that's why i used $setUninon.

bc110402922 Over a year ago

Thanks, Its work for me. I get multiple documents. how I can make one? document 1: { _id: abcdef, name: "foo", time: [1234], doc: [1234] } document 2 { _id: alexa, name: "alexa", time: [1234], doc: [1234] } Expected output { time[1234], alexa[1234], foo[1234] }

turivishal Over a year ago

You mean you need to combine all documents in single? just share a playground link with your data.

bc110402922 Over a year ago

playground. yes, I want to combine all documents into single documents.

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