CODEWITHSUNDEEP
javascriptgoogle-maps-api-3
Below the Radar
Below the Radar

Reputation: 7635

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();
        alert(allMarkers.length)
        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) {
                    allMarkers[j].setOptions({
                        icon : "http://labs.google.com/ridefinder/images/mm_20_white.png",
                        shapeId:createdShapes[i].id
                    });
                }else{
                    allMarkers[j].setOptions({
                        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].number)
          }
    }

There are 32600 numbers total in allMarkers.number among 3505 objects. The first time I call the function I get:

allTotal= [
   Object { number=32598,  shapeId='shapeid0'},
   Object { number=2,  shapeId='shapeid1'}
]

where shapeid0 is not selected. The second time I call the function without changing anything, I get:

allTotal= [
   Object { number=65193,  shapeId='shapeid0'},
   Object { number=2,  shapeId='shapeid1'}
]

And the third time:

allTotal= [
   Object { number=97788,  shapeId='shapeid0'},
   Object { number=2,  shapeId='shapeid1'}
]

Upvotes: 0

Views: 246

Answers (1)

Bergi
Bergi

Reputation: 664185

Your code is a bit oddly formatted. However, the problem is that inside the expression res.__array.push(res[obj.shapeId] = obj); you assign the object itself to the res, not a clone. With res[obj.shapeId].number += obj.number; you then manipulate the original object, which is why the results grow in subsequent calls.

Better:

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

Upvotes: 2

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