How to check if all values in an array are the same mongodb aggregation?

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How to check if all values in an array are the same mongodb aggregation? Say I have an array ["a","a","a","a","a"] in an aggregation stage. How do I check if all the values are the same using mongodb aggregation?

And if there is a different approach for an array of objects [{a:"a",b:"b"},{a:"c",b:"d"}]. How do I check if all the values of a given object property are the same for all objects in an array using mongodb aggregation?

I know in javascript I can use array.every() is there an equivalent in mongodb?

aggregation-framework mongodb arrays
1 Answers

You can try using $allElementsTrue:

db.collection.aggregate([
    {
        $project: {
            areSame: {
                $allElementsTrue: {
                    $map: {
                        input: "$key",
                        in: {
                            $eq: [ "$$this", { $arrayElemAt: [ "$key", 0 ] } ]
                        }
                    }
                }
            }
        }
    }
])

Mongo Playground

same solution should work for objects

user_62389770
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