get a count of array property values in MongoDB

Question

Given data like

[
    { _id:1, data:["abc", "def", "hij", "klm", "nop"]},
    { _id:2, data:["abc", "def", "hij"]},
    { _id:3, data:["abc", "hij"]},
    { _id:4, data:["abc", "def", "hij", "klm", "nop"]},
    { _id:5, data:["def", "hij", "klm"]},
]

I am trying to get a query result like

[
    { "abc": 4 },
    { "def": 4 },
    { "hij": 5 },
    { "klm": 3 },
    { "nop": 2 },
]

where the number is the count of each data property array string value.

I have been working on it from an aggregate pipeline approach, but it seems like there should be an easier way.

Is that data available in javascript? would you accept an answer using javascript's array methods? — Shidersz
– Shidersz, Commented Jan 31, 2019 at 20:39
I have been working on constructing the query in the mongoDB CLI client, but the end goal environment is a nodejs app. I am using javascript — stackuser83
– stackuser83, Commented Jan 31, 2019 at 20:41
I can only offers a solution where you process the data on the Javascript side, but I believe you want it to comes already processed to Javascript. Anyway, I suggest to add what you have tried to far... — Shidersz
– Shidersz, Commented Jan 31, 2019 at 20:46

p.s.w.g · Accepted Answer · 2019-01-31 21:02:41Z

3

You ought to be able to do this with an aggregation pipeline with $unwind + $group. For example:

db.col.aggregate([{$unwind:"$data"}, {$group: {_id: "$data", data: {$sum: 1}}}])

Returns:

{ "_id" : "nop", "data" : 2.0 }
{ "_id" : "abc", "data" : 4.0 }
{ "_id" : "def", "data" : 4.0 }
{ "_id" : "hij", "data" : 5.0 }
{ "_id" : "klm", "data" : 3.0 }

answered Jan 31, 2019 at 21:02

p.s.w.g

150k31 gold badges307 silver badges339 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

stackuser83 Over a year ago

simply exactly. I found unwind's applicability moments after you posted this answer

Collectives™ on Stack Overflow

get a count of array property values in MongoDB

1 Answer 1

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related