How to match and group array elements with the max value in MongoDB aggregation?

For this, use $group along with $max in MongoDB. Let us create a collection with documents −

> db.demo510.insertOne( ... { ...    details:[ ...       { ...          Name:"Chris", ...          Score:56 ...       }, ...       { ...          Name:"David", ...          Score:45 ...       } ...    ] ... } ... ); {    "acknowledged" : true,    "insertedId" : ObjectId("5e8845fa987b6e0e9d18f582") } > db.demo510.insertOne( ... { ...    details:[ ...       { ...          Name:"Chris", ...          Score:56 ...       }, ...       { ...          Name:"David", ...          Score:47 ...       } ...    ] ... } ... ); {    "acknowledged" : true,    "insertedId" : ObjectId("5e8845fb987b6e0e9d18f583") } > db.demo510.insertOne( ... { ...    details:[ ...       { ...          Name:"Chris", ...          Score:45 ...       }, ...       { ...          Name:"David", ...          Score:91 ...       } ...    ] ... } ... ); {    "acknowledged" : true,    "insertedId" : ObjectId("5e8845fb987b6e0e9d18f584") }

Display all documents from a collection with the help of find() method −

> db.demo510.find();

This will produce the following output −

{ "_id" : ObjectId("5e8845fa987b6e0e9d18f582"), "details" : [ { "Name" : "Chris", "Score" : 56 }, { "Name" : "David", "Score" : 45 } ] } { "_id" : ObjectId("5e8845fb987b6e0e9d18f583"), "details" : [ { "Name" : "Chris", "Score" : 56 }, { "Name" : "David", "Score" : 47 } ] } { "_id" : ObjectId("5e8845fb987b6e0e9d18f584"), "details" : [ { "Name" : "Chris", "Score" : 45 }, { "Name" : "David", "Score" : 91 } ] }

Following is the query to match and group array elements with the max value in aggregation −

> db.demo510.aggregate([ ... { "$project": { ...    "details": { ...       "$arrayElemAt": [ ...          { "$filter": { ...             "input": "$details", ...             "as": "res", ...             "cond": { ...                "$eq": [ ...                   "$$res.Score", ...                   { "$max": { ...                      "$map": { ...                         "input": "$details", ...                         "as": "out", ...                         "in": "$$out.Score" ...                      } ...                   }} ...                ] ...             } ...          }}, ...          0 ...       ] ...    } ... }}, ... { "$group": { ...    "_id": "$details.Name", ...    "Name": { "$first": "$details.Name" }, ...    "count": { "$sum": 1 } ... }} ... ])

This will produce the following output −

{ "_id" : "David", "Name" : "David", "count" : 1 } { "_id" : "Chris", "Name" : "Chris", "count" : 2 }