CODEWITHSUNDEEP
mongodbaggregation-framework
Net_Raider
Net_Raider

Reputation: 185

Retrieve other fields from the document corresponding to $max

I have a collection of documents like these:

{
    "_id": numeric-id, 
    "timestamp": a-timestamp, 
    "odd1": "3.45", 
    "odd2": "1.95", 
    "odd3": "4.05", 
    "source": "a"
}

I managed to aggregate the records using this snippet:

{
    $group: {
        _id: {tm: "$timestamp"},
        odd1: {$max: "$odd1"},
        odd2: {$max: "$odd2"},
        odd3: {$max: "$odd3"}
    }
}

In addition to the maximum odd of each cathegory, I also need the corresponding field 'source' that provides the maximum odd. Is there a way for asking this to mongo?

Upvotes: 2

Views: 66

Answers (1)

sergiuz
sergiuz

Reputation: 5529

You can't do that in MongoDB, but you can do a second query, to find out out the source of each maxx odd, at all timestamps:

var agg = db.collection.aggregate(
    {
        $group: {
            _id: {tm: "$timestamp"},
            odd1: {$max: "$odd1"},
            odd2: {$max: "$odd2"},
            odd3: {$max: "$odd3"}
        }
    }
);


while (agg.hasNext()) {
    var o = agg.next();
    var timestamp_odd1 = db.collection.findOne({timestamp: o['_id']['tm'],odd1:o['odd1']});
    var timestamp_odd2 = db.collection.findOne({timestamp: o['_id']['tm'],odd2:o['odd2']});
    var timestamp_odd3 = db.collection.findOne({timestamp: o['_id']['tm'],odd3:o['odd3']});
    print ("timestamp: ", o._id.tm,'  max_odd1:', timestamp_odd1['odd1'], '  ', 'source: ', timestamp_odd1['source']) ;
    print ("timestamp: ", o._id.tm,'  max_odd2:', timestamp_odd2['odd2'], '  ', 'source: ', timestamp_odd2['source']) ;
    print ("timestamp: ", o._id.tm,'  max_odd3:', timestamp_odd3['odd3'], '  ', 'source: ', timestamp_odd3['source']) ;
}

Upvotes: 1

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