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  1. Core Server
  2. SERVER-23816

Add $sortByCount aggregation stage

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    • Fully Compatible
    • Query 16 (06/24/16)

      Syntax

      { $sortByCount: <arbitrary non-object expression, see 'Behavior' for why> }

      Examples

      > db.example.insert([
  {_id: 0, x: 1},
  {_id: 1, x: 2},
  {_id: 2, x: 1},
  {_id: 3, x: 0}
]);
> db.example.aggregate([{$sortByCount: "$x"}])
{_id: 1, count: 2}
{_id: 0, count: 1}
{_id: 2, count: 1}

// Example #2
> db.example.drop();
> db.example.insert([
  {_id: 0, x: 1.4},
  {_id: 1, x: 2.3},
  {_id: 2, x: 1.1},
  {_id: 3, x: 0.5}
]);
// Note this is an expression, so does not count as an "object" for the sake of erroring.
> db.example.aggregate([{$sortByCount: {$floor: "$x"}}])
{_id: 1, count: 2}
{_id: 0, count: 1}
{_id: 2, count: 1}

// Example #3
> db.example.aggregate([{$sortByCount: {field1: "$x", field2: "$y"}}])
Error!

      Behavior

      • This stage is syntactic sugar for the following: 
        {
  $group: {
    _id: <expression>,
    count: {$sum: 1}
  }
},
{$sort: {count: -1}}
      • We restrict the expression to not be an object so that we might be able to add further arguments to $sortByCount in the future.

            Assignee:
            sally.mcnichols Sally McNichols
            Reporter:
            charlie.swanson@mongodb.com Charlie Swanson
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              Created:
              Updated:
              Resolved: