javascript - Get sums by grouping a collection in Meteor -

i have collection fields: number, a, b, c.

i want divide collection in 3 based on number , separate sums of a, b, , c each group division.

i have done with

function sumlist(amountlist) {   return _.reduce(amountlist, function(sum, amount) {     return sum + amount;   }, -1); }  // cursors var group1 = groups.find({ number: { $lte: 32 } }).fetch(); var group2 = groups.find({ number: { $gte: 33, $lte: 70 } }).fetch(); var group3 = groups.find({ number: { $gte: 71 } }).fetch();  // sums group1 var group1suma = sumlist(_.pluck(group1, "a")); var group1sumb = sumlist(_.pluck(group1, "b")); var group1sumc = sumlist(_.pluck(group1, "c"));  // sums group2 var group2suma = sumlist(_.pluck(group2, "a")); var group2sumb = sumlist(_.pluck(group2, "b")); var group2sumc = sumlist(_.pluck(group2, "c"));  // sums group3 var group3suma = sumlist(_.pluck(group3 "a")); var group3sumb = sumlist(_.pluck(group3, "b")); var group3sumc = sumlist(_.pluck(group3, "c")); 

it works think code ugly.

i wonder if can done smart mapping. besides, guess might have bad performance.

how can these sums optimized?

use aggregation framework have $match pipeline operator filter collection on number field. $group pipeline step groups filtered input documents , applies accumulator expression $sum each field sums.

your pipeline this:

var pipeline = [     {         "$match": { "number": { "$lte": 32 } } /* group1 filter */     },     {         "$group": {             "_id": 0,             "suma": { "$sum": "$a" },             "sumb": { "$sum": "$b" },             "sumc": { "$sum": "$c" }         }     } ]; 

you can add meteorhacks:aggregate package implement aggregation in meteor:

add app with

meteor add meteorhacks:aggregate 

since package exposes .aggregate method on mongo.collection instances, can call method resulting array document has sums. example

if (meteor.isserver) {     var coll = new mongo.collection('collectionname');     meteor.methods({         sumlist: function (filter) {             var pipeline = [                 {                     "$match": filter                 },                 {                     "$group": {                         "_id": 0,                         "suma": { "$sum": "$a" },                         "sumb": { "$sum": "$b" },                         "sumc": { "$sum": "$c" }                     }                 }             ];                       var result = coll.aggregate(pipeline);             return result[0];         }     });  }  if (meteor.isclient) {     // filters     var group1 = { "number": { "$lte": 32 } };     var group2 = { "number": { "$gte": 33, "$lte": 70 } };     var group3 = { "number": { "$gte": 71 } };      meteor.call('sumlist', group1, callback);     //meteor.call('sumlist', group2, callback);     //meteor.call('sumlist', group3, callback);      function callback(err, result) {         console.log(result)     } }