Mongo $group array elements based on input array

Question

My collection has following format -

{
 "title" : "Seasonal", 
 "state" : "Maharashtra",
 "fruits" : [ "banana", "orange", "jackfruit", "mango", "tamarind"]
} 
{
 "title" : "Seasonal", 
 "state" : "Karnataka",
 "fruits" : [ "banana", "avacado", "blackberry", "coconut", "grape"]
}
{
 "title" : "Alltime", 
 "state" : "Karnataka",
 "fruits" : [ "banana", "lemon", "pomegranate", "pineapple"]
}

And my query is like

db.fruits.aggregate([{"$match": {"state": "Karnataka", "fruits": {"$elemMatch": {"$in": ["banana","coconut"]}}}},{ $unwind : "$fruits" },{"$group" : {"_id" : "$fruits","count" : {"$sum":1}}}])

And getting Output as -

{ "_id" : "pineapple", "count" : 1 }
{ "_id" : "lemon", "count" : 1 }
{ "_id" : "grape", "count" : 1 }
{ "_id" : "pomegranate", "count" : 1 }
{ "_id" : "coconut", "count" : 1 }
{ "_id" : "blackberry", "count" : 1 }
{ "_id" : "avacado", "count" : 1 }
{ "_id" : "banana", "count" : 2 }

Instead in return what I want is input fruit names with count of their occurance. i.e.

{ "_id" : "coconut", "count" : 1 }
{ "_id" : "banana", "count" : 2 }

Will you please tell me, How to $group these array elements?

s7vr · Accepted Answer · 2018-03-01 13:57:05Z

3

Use below aggregation. You are missing a $match stage after $unwind.

Initial match only filters document where there exists fruits array with at least one fruit from matching input fruits array.

Once you $unwind it unwinds all the fruits which also includes other fruits. So when you use second match you filter the fruits to only contain fruits matching from input fruits array.

db.fruits.aggregate([
  {"$match":{"state":"Karnataka","fruits":{"$elemMatch":{"$in":["banana","coconut"]}}}},
  {"$unwind":"$fruits"},
  {"$match":{"fruits":{"$in":["banana","coconut"]}}},
  {"$group":{"_id":"$fruits","count":{"$sum":1}}}
])

answered Mar 1, 2018 at 13:57

s7vr

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6 Comments

Priyanka Over a year ago

Will you please help me with this. I want a counts of fruits containing banana, coconunt, [banana, coconut](no $elementMatch i.e $all) separately

s7vr Over a year ago

Not sure I follow you. You want count of all fruits together ?

Priyanka Over a year ago

No no. I want to query array of array.. like ["banana, coconut, lemon"] , ["orange", "jackfruit"] returning array with counts opposite to $elementMatch

s7vr Over a year ago

I see. You can write a or condition with each condition being in criteria matching each array. Something like {$or:[{$in:first set}, repeat for all sets]}

Priyanka Over a year ago

But Using $or will give me count for only one array condition. I want it for all at once like above output.

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