MongoDB distinct aggregation

mongodb distinct
Lemonio picture Lemonio · May 4, 2013 · Viewed 100.8k times · Source

I'm working on a query to find cities with most zips for each state:

db.zips.distinct("state", db.zips.aggregate([ {$group:{_id:{state:"$state", city:"$city"},numberOfzipcodes:{$sum:1}}}, {$sort:{numberOfzipcodes:-1}}]))

The aggregate part of the query seems to work fine, but when I add the distinct I get an empty result.

Is this because I have state in the id? Can I do something like distinct("_id.state ?

Answer

dam1 picture dam1 · Feb 3, 2016

You can use $addToSet with the aggregation framework to count distinct objects.

For example:

db.collectionName.aggregate([{
    $group: {_id: null, uniqueValues: {$addToSet: "$fieldName"}}
}])

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