How to concatenate arrays from multiple documents in MongoDB?

Question

Let's say I have a collection called 'people' with the following documents:

{
    "name": "doug",
    "colors": ["blue", "red"]
}

{
    "name": "jack",
    "colors": ["blue", "purple"]
}

{
    "name": "jenny",
    "colors": ["pink"]
}

How would I get a concatenated array of all the colors subarrays, i.e.?

["blue", "red", "blue", "purple", "pink"]

Anuj Aneja · Accepted Answer · 2013-09-02 17:15:16Z

34

Well, Try should work fine for you!!

db.people.distinct("colors")

answered Sep 2, 2013 at 17:15

Anuj Aneja

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3 Comments

Mithril Over a year ago

simple and efficient! this answer should be the accepted one.

zaboco Over a year ago

very good, exactly what I needed; it is also good to know that you can pass an optional query to distinct to filter out the results. source

Lucas Ross Over a year ago

This doesn't answer the question. This returns only the distinct colors, while the accepted answer returns all the arrays concatenated.

Yevgeniy Anfilofyev · Accepted Answer · 2014-11-18 14:48:20Z

30

Try to use aggregate:

db.people.aggregate([
  {$unwind:"$colors"},
  {$group:{_id:null, clrs: {$push : "$colors"} }},
  {$project:{_id:0, colors: "$clrs"}}
])

Result:

{
"result" : [
    {
        "colors" : [
            "blue",
            "red",
            "blue",
            "purple",
            "pink"
        ]
    }
],
"ok" : 1
}

Updated

If you want to get unique values in result's array, you could use $addToSet operator instead of $push in the $group stage.

edited Nov 18, 2014 at 14:48

answered Sep 2, 2013 at 17:35

Yevgeniy Anfilofyev

4,85728 silver badges27 bronze badges

2 Comments

viren Over a year ago

HI but if i need unique value in result how i will achieve that as this will give duplicate entry in this array

Yevgeniy Anfilofyev Over a year ago

For sure. To do this you could change $push operator with $addToSet in {$group:{_id:null, clrs: {$push : "$colors"} }}, string.

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