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

1. Registered User
Join Date
Dec 2012
Posts
8

## 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.

Code:
```    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) {
allMarkers[j].setOptions({
shapeId:createdShapes[i].id
});
}else{
allMarkers[j].setOptions({
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. Registered User
Join Date
Dec 2012
Posts
90
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

Code:
```<script>
var x = 0;
{
x += 10;
}
</script>```
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. Registered User
Join Date
Dec 2012
Posts
8
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.

Better:

Code:
```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) {
});```

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