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How to MapReduce collection to join an array of all values ​​in the field contai...

 3 years ago
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How to MapReduce collection to join an array of all values ​​in the field containing the array

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I have the following schema in the database:

{
    id: 12345;
    friends: [123,345,678,908]
},
{
    id: 908;
    friends: [123,345]
}

Is there a way to get an array of all unique friends IDs from the entire collection?

To get distinct friends values you do not need to write map/reduce job.

Just run:

> db.collection.distinct("friends")
[ 123, 345, 678, 908 ]

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