Question 116726 in Mongodb Question posted in
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Mongodb – How to sort strings in a arbitrary or given order in Mongo Aggregation Pipeline?

I have an aggregation pipeline that returns 20 tuples with known _id’s:

[ { _id: 'AA', value: 5 },
  { _id: 'CD', value: 2 },

How to create a pipeline stage to order them in an arbitrary order?

For example ‘CD’, ‘AA’, ‘EF’, ‘BC’.

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2

Answers


  1. Chosen as BEST ANSWER
    0

    Similar to Takis' answer.

             { '$addFields': {
            'order': { '$indexOfArray': [ ['CD', 'AA', 'EF', 'BC'...], '$_id' ] }}},
         { '$sort': { 'order': 1 }}]

  2. 0

    Query1

    • this is for random order
    • add a temp field with a random value
    • sort by it
    • unset the temp field

    *i don’t know if this is the optimal way to do it, but it works

    Playmongo

    aggregate(
[{"$set": {"rand": {"$rand": {}}}},
 {"$sort": {"rand": 1}},
 {"$unset": ["rand"]}])

    Query2

    • this in to apply a specific order for example "CD then AA etc"
    • add a new field that contains the index of the _id from the array that defines the order
    • sort by it
    • unset it

    Playmongo

    aggregate(
[{"$set": {"key": {"$indexOfArray": [["CD", "AA"], "$_id"]}}},
 {"$sort": {"key": 1}},
 {"$unset": ["key"]}])
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