CODEWITHSUNDEEP
mongodbaggregation-framework
Nic Cottrell
Nic Cottrell

Reputation: 9685

Possible to use $sum with computed field value in MongoDB aggregation framework?

I'm doing a fuzzy match to an input sentence, and I currently have a step in the AF like this:

{ "$group" : { "_id" : "$_id" , "score" : { "$sum" : 1}}}

but I'd like to be able to score shorter matches higher and want to do something like:

{ "$group" : { "_id" : "$_id" , "score" : { "$sum" : "1 / $length"}}}

Is something like this possible?

Upvotes: 0

Views: 35

Answers (2)

amitava
amitava

Reputation: 505

I guess you want something like this. the default "_id" values are unique, so probably you want to group some other parameter. So I used another parameter idd, instead of _id here.

> db.tmp1.aggregate({'$group':{'_id':'$idd', 'count':{'$sum':1}   }},{ $project : { _id: 1, suminv :{$divide:[1, '$count']  } } }  );


{ "_id" : 2, "suminv" : 0.3333333333333333 }{ "_id" : 1, "suminv" : 0.5 }

> db.tmp1.find();
{ "_id" : ObjectId("572a5a74024dc1f2fe4b432b"), "idd" : 1, "score" : 2 }
{ "_id" : ObjectId("572a5a79024dc1f2fe4b432c"), "idd" : 1, "score" : 1 }
{ "_id" : ObjectId("572a5a82024dc1f2fe4b432d"), "idd" : 2, "score" : 1 }
{ "_id" : ObjectId("572a5a86024dc1f2fe4b432e"), "idd" : 2, "score" : 2 }
{ "_id" : ObjectId("572a5a8e024dc1f2fe4b432f"), "idd" : 2, "score" : 3 }

Upvotes: 0

lesingerouge
lesingerouge

Reputation: 1168

Yes, it should be possible (assuming $length is a field name in your documents), but the command should look like this:

{ "$group" : { "_id" : "$_id" , "score" : { $sum : {$divide: [1, "$length"]}}}}

You can find more details about possible math expressions on this page.

Upvotes: 1

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