getting count based on array of element in mongoDB

Question

im trying to get count of documents based on array of element. My collection have documents like...

[
   {pid: "p001", items :["apple","bat","cat"]},
   {pid: "p002", items :["apple","cat","bat"]},
   {pid: "p003", items :["apple","bat","cat","dog"]},
   {pid: "p004", items :["apple","bat","cat","dog"]}
]

i write a mongo aggregation query like

db.collection_name.aggregate([
   {$group : {_id: "$items", count: {$sum : 1}}},
   {$project : { _id: 0, items: "$_id" , count: 1 } }
])

im getting output like

[
   {items: ["apple","bat","cat"], count: 1},
   {items: ["apple","cat","bat"], count: 1},
   {items: ["apple","bat","cat","dog"], count: 2}
]

but i want my output like

[
    {items: ["apple","bat","cat"], count: 2},
    {items: ["apple","bat","cat","dog"], count: 2}
]

can you help me out of this.....

Ashh · Accepted Answer · 2019-01-27 08:58:04Z

1

You need to $sort the items array in order to make it similar to the other items array and then can $group with the items

db.collection.aggregate([
  { "$unwind": "$items" },
  { "$sort": { "items": 1 }},
  { "$group": { "_id": "$pid", "items": { "$push": "$items" }}},
  { "$group": { "_id": "$items", "count": { "$sum": 1 }}},
  { "$project": { "_id": 0, "items": "$_id", "count": 1 }}
])

answered Jan 27, 2019 at 8:58

Ashh

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