如何按每个id对数组中的对象求和，计算平均和，按条件顺序设置

Question

I am using mongoose find() method to get all records from db. After that I want to create new sorted array or array of objects. Those record can have same parameter name like "startNum" . How can I have summed values with same parameter and counted average value of each?

I tried using Javascript for loops but I have got only arrays with this result values from db with this same "startNum" parameter, but few of them have empty spaces that I don't want - it's like [2, , ,5] . I think it can be done easier. It would be nice if it was made using underscorejs.

Here is my try:

stars.find({}, function(error, result) {
               if(error) {
                 console.log(error);
               }
               var tmp = {};
               var a = [];
               One = {};
               var snOne = [];
               Two = {};
               var snTwo = [];
               Three = {};
               var snThree = [];
               var Four = {};
               var snFour = [];
               var Five = {};
               var snFive = [];

              for (var s = 0; s < result.length; s ++) {
                if (result[s].startingNumber === 1) {
                  snOne[0] = 1; // numer startowy konia
                  snOne[s+1]=(result[s].categoryOne + result[s].categoryTwo + result[s].categoryThree + result[s].categoryFour + result[s].categoryFive);
                }


                 if (result[s].startingNumber === 2) {
                  for (var q = 0; q < result.length; q ++) {
                  snTwo[0] = 2;
                  snTwo[q+1]=(result[q].categoryOne + result[q].categoryTwo + result[q].categoryThree + result[q].categoryFour + result[q].categoryFive);
                  }
                }

              for (var w = 0; w < result.length; w ++) {
                 if (result[w].startingNumber === 3) {
                  snThree[0] = 3;
                  snThree[w+1]=(result[w].categoryOne + result[w].categoryTwo + result[w].categoryThree + result[w].categoryFour + result[w].categoryFive);
                }
              }
                for (var e = 0; e < result.length; e ++) {
                 if (result[e].startingNumber === 4) {
                  snFour[0] = 4;
                  snFour[e+1]=(result[e].categoryOne + result[e].categoryTwo + result[e].categoryThree + result[e].categoryFour + result[e].categoryFive);
                }
              }
                for (var r = 0; r < result.length; r ++) {
                 if (result[r].startingNumber === 5) {
                  snFive[0] = 5;
                  snFive[r+1]=(result[r].categoryOne + result[r].categoryTwo + result[r].categoryThree + result[r].categoryFour + result[r].categoryFive);
                }
              }
              }// ..

I know this sorting Underscore method, that can be useful, but dont know exactly how to do this.

var sorted = _.sortBy(a, function(num) { return num; });

To sum up I want to have counted average value for each startingNum category. For example array of objects

first object

{
    startingNum: 1,
counted_Average_Of_All_Existing_In_DataBase_Categories_From_One_To_Five_For_startingNum1: value
}

Those mongoose results looks like:

[ {
categoryFive: 1,
categoryFour: 1,
categoryThree: 1,
categoryTwo: 1,
categoryOne: 1,
startingNumber: 1},... ]

I think it would be much better using underscorejs . Can someone help? I can't figure out how to make it right.

Answer 1

I see you have already written javascript loop code to group your documents by startingNumber and then sum the category values, and you just wanted input on how best to sort that using underscore.js.

However, I believe it would be better and simpler to use MongoDB's aggregation framework to do the grouping, summing and sorting for you. You had also said you wanted a counted average so my sample code calculates count and average too.

If I load your sample data:

db.catdata.insert([
  {categoryFive:   1, categoryFour:   1, categoryThree:   1, 
   categoryTwo:    1, categoryOne:    1, startingNumber:  1},
  {categoryFive:   2, categoryFour:   1, categoryThree:   2, 
   categoryTwo:    1, categoryOne:    2, startingNumber:  1},
  {categoryFive:   1, categoryFour:   1, categoryThree:   1, 
   categoryTwo:    1, categoryOne:    1, startingNumber:  2},
  {categoryFive:  20, categoryFour:   1, categoryThree:  20, 
   categoryTwo:   20, categoryOne:   20, startingNumber:  1},
  {categoryFive: 100, categoryFour: 100, categoryThree: 100, 
   categoryTwo:  100, categoryOne:  100, startingNumber:  2}
]) ;

then this statement:

db.catdata.aggregate([
    {"$project" : {"startingNumber":1,
           "cats1to5":{$add:["$categoryFive", "$categoryFour", 
           "$categoryThree", "$categoryTwo",  "$categoryOne"]}
                  }
    }
   ,{"$group": {"_id"  : "$startingNumber",  "cntCat":{$sum:1},
                "totCat":{$sum:"$cats1to5"}, "avgCat":{$avg:"$cats1to5"}
               }
    }
   ,{$sort : {startingNumber:1}}
]);

produces this output:

{ "_id" : 2, "cntCat" : 2, "totCat" : 505, "avgCat" : 252.5 }
{ "_id" : 1, "cntCat" : 3, "totCat" : 94, "avgCat" : 31.333333333333332 }

Answer 2

I'm assuming you wanted to find the total score across all categories grouped by the starting number. If so, here goes the solution using underscore.js

// group by startingNumber
// each group will have multiple objects denoted by 'objs'
var grouped = _.chain(data).groupBy('startingNumber').map(function (objs, startNum) {
    // iterate through the objects for the current starting number
    var score = _.chain(objs).map(function (obj) {
        // remove all keys which are not starting with category
        var obj    = _.pick(obj, function (value, key) {
            return key.indexOf('category') !== -1;
        });
        var scores = _.values(obj); // get the scores for each category

        // compute the sum across all categories for this object
        return _.reduce(scores, function (memo, categoryScore) {
            return memo + categoryScore;
        }, 0);
        // compute the sum across all objects for this group
    }).reduce(function (memo, value) {
        return memo + value;
    }, 0).value();

    return {
        start: startNum,
        score: score
    };
}).value();