Return a max value of an array with aggregate request in mongodb

Question

hello i have this json

db.people.insert({
    "ad" : "noc2",
    "createdDate" : ISODate(),
    "list" : [
            {
                    "id" : "p45",
                    "date" : ISODate("2014-01-01T12:18:30.568Z"),
                    "value3" : 21,
                    "value1" : 77,
                    "value2" : 489
            },
            {
                    "id" : "p6",
                    "date" : ISODate("2013-07-18T12:18:30.568Z"),
                    "value3" : 20,
                    "value1" : 20,
                    "value2" : 7
            },
            {
                   "id" : "4578",
                    "date" : ISODate("2013-07-18T12:18:30.568Z"),
                    "value3" : 21,
                    "value1" : 300,
                    "value2" : -319
            }
   ]

})

and i'd like get a max value of my array. For example, i want a json as this :

"result" : [ { "_id" : "p45", "value" : 587 } ]

and my aggregate request who doesn't work is : db.test1.aggregate({$match: "ad":"noc2"},{$unwind: '$list'},{$group: {_id: '$ad', list: {recommand: {$max: '$list'}}}});

Victoria Malaya · Accepted Answer · 2013-07-22 14:37:18Z

2

The answer contains a couple of issues in query syntax, but mostly it works. Below you can find fixed query:

db.people.aggregate(
  {$match:{ad:"noc2"}},
  {$unwind:"$list"},
  {$project:{_id:0, _id:"$list.id", "value":{$add:["$list.value1","$list.value2","$list.value3"]}}},
  {$sort:{value:-1}},
  {$limit:1}
);

edited Jul 22, 2013 at 14:37

answered Jul 22, 2013 at 14:12

Victoria Malaya

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1 Comment

jonn Over a year ago

thanks for your response but if i have too much value, how i can to do without write all values in my array ? Because i can't to do this because i must keep the value name and his value, and the value name can change.Secondly, it may be that I have fifty thousand values

Yevgeniy Anfilofyev · Accepted Answer · 2013-07-22 17:21:16Z

1

Try this:

db.people.aggregate([
  {$match:{ad:"noc2"}},
  {$unwind:"$list"},
  {$project:{_id:0, _id":"$list.id", "value":{$add:["$list.value1","$list.value2","$list.value3"]}}},
  {$sort:{value:-1},
  {$limit:1}
])

Output:

{ "result" : [ { "_id" : "p45", "value" : 587 } ], "ok" : 1 }

edited Jul 22, 2013 at 17:21

answered Jul 22, 2013 at 11:46

Yevgeniy Anfilofyev

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3 Comments

jonn Over a year ago

thanks for your response but if i have too much value, how i can to do without write all values in my array ?

Yevgeniy Anfilofyev Over a year ago

Maybe it would be better to keep all of them into one array, something like "values": [21, 77, 489, ...] and then just sum them...

jonn Over a year ago

i can't to do this because i must keep the value name and his value, and the value name can change.Secondly, it may be that I have fifty thousand values.

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