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Thread: Sum values of attribute when the value of an other attribute is the same

  1. #1
    Join Date
    Dec 2012

    Sum values of attribute when the value of an other attribute is the same

    I have an array of objects like this one:

    {'shapeId': 'shapeid1', 'latlong': '45.42342,-65.23424', 'number': 5}

    I want the sum of the values of the attribute "number" when the value of the attribute "shapeId" is the same.

    Is there a built in method for that? Thank you!

    What I tried so far is this, using reduce() method, but the results are odd when the function is called many times.

        function selectMarkersInPoly() {
            allTotal = new Array();
            for (var i=0; i < createdShapes.length; i++) {
            for (var j=0; j < allMarkers.length; j++){
                    var latlong = allMarkers[j].getPosition();
                    if(google.maps.geometry.poly.containsLocation(latlong, createdShapes[i]) == true) {
                            icon : "http://labs.google.com/ridefinder/images/mm_20_white.png",
                            icon : "http://labs.google.com/ridefinder/images/mm_20_red.png",
                            shapeId: 'shapeid0'
        allTotal = allMarkers.reduce(function(res, obj) {
            if (!(obj.shapeId in res)){
            res.__array.push(res[obj.shapeId] = obj);
            }else {
            res[obj.shapeId].number += obj.number;
            return res;
                }, {__array:[]}).__array
                    .sort(function(a,b) { return b.shapeId - a.shapeId;
            for (var j=0; j < allTotal.length; j++) {
            alert(allTotal[j].shapeId + ': ' + allTotal[j].nbr_electeur)
    //There is 32600 number in total in allMarkers.number in 3505 objects
    //first time i call the function, allTotal= [Object { number=32598,  shapeId='shapeid0'}, Object { number=2,  shapeId='shapeid1'}] where shapeid0 are not selected
    //second time i call that function without changing anything, allTotal= [Object { number=65193,  shapeId='shapeid0'}, Object { number=2,  shapeId='shapeid1'}]
    //third time: allTotal= [Object { number=97788,  shapeId='shapeid0'}, Object { number=2,  shapeId='shapeid1'}]

  2. #2
    Join Date
    Dec 2012
    It looks like you are always appending to the variable aka +=. If you don't reset it back to zero when you call the function then you will just get an incrementally large result. Like if I did

      var x = 0;
      function AddTen()
         x += 10;
    X would get ten larger every time I called the function. If I wanted X to only be 10 then I would have to put the x = 0 inside the function. (or just make the function x = 10, but I'm sure you see my point)

  3. #3
    Join Date
    Dec 2012
    Yes you are rigth. The problem is that inside the expression res.__array.push(res[obj.shapeId] = obj); I assign the object itself to the res, not a clone. With res[obj.shapeId].number += obj.number; then it manipulates the original object, which is why the results grow in subsequent calls.


    var numberSums = allMarkers.reduce(function(res, obj) {
        var id = obj.shapeId;
        if (id in res)
            res[id] += obj.number;
            res[id] = obj.number;
        return res;
    }, {});
    Object.keys(numberSums).sort(function(a,b){return a-b;}).forEach(function(id) {
        alert(id+": "+numberSums[id]);

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