Question

180

Sum JavaScript object propertyA values with the same object propertyB in an array of objects

rated 0 times [ 187] [ 7] / answers: 1 / hits: 24286 / 11 Years ago, mon, october 7, 2013, 12:00:00

How would one take a JavaScript array of objects, such as

objArr = [

    {key:"Mon Sep 23 2013 00:00:00 GMT-0400", val:42},

    {key:"Mon Sep 24 2013 00:00:00 GMT-0400", val:78},

    {key:"Mon Sep 25 2013 00:00:00 GMT-0400", val:23},

    {key:"Mon Sep 23 2013 00:00:00 GMT-0400", val:54} // <- duplicate key

]

and merge duplicate keys by summing the values?

In order to get something like this:

reducedObjArr = [

    {key:"Mon Sep 23 2013 00:00:00 GMT-0400", val:96},

    {key:"Mon Sep 24 2013 00:00:00 GMT-0400", val:78},

    {key:"Mon Sep 25 2013 00:00:00 GMT-0400", val:23}

]

I have tried iterating and adding to a new array, but this didn't work:

var reducedObjArr = [];

var item = null, key = null;

for(var i=0; i<objArr.length; i++) {

    item = objArr[i];

    key = Object.keys(item)[0];

    item = item[key];



    if(!result[key]) {

        result[key] = item;

    } else {

       result[key] += item;

    }

}a

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katelinb

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3 Years ago

answered 11 Years ago stacie · Accepted Answer

You should be assigning each object not found to the result with its .key property.

If it is found, then you need to add its .val.

var temp = {};

var obj = null;

for(var i=0; i < objArr.length; i++) {

   obj=objArr[i];



   if(!temp[obj.key]) {

       temp[obj.key] = obj;

   } else {

       temp[obj.key].val += obj.val;

   }

}

var result = [];

for (var prop in temp)

    result.push(temp[prop]);

Also, part of the problem was that you were reusing the item variable to reference the value of .key, so you lost reference to the object.