Sum javascript object propertyA values with same object propertyB in array of objects
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.
Rather than using a for loop and pushing values, you can directly use map and reduce:
let 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}
];
// first, convert data into a Map with reduce
let counts = objArr.reduce((prev, curr) => {
let count = prev.get(curr.key) || 0;
prev.set(curr.key, curr.val + count);
return prev;
}, new Map());
// then, map your counts object back to an array
let reducedObjArr = [...counts].map(([key, value]) => {
return {key, value}
})
console.log(reducedObjArr);You could use a hash table for the grouping by key.
var array = [{ 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}],
grouped = [];
array.forEach(function (o) {
if (!this[o.key]) {
this[o.key] = { key: o.key, val: 0 };
grouped.push(this[o.key]);
}
this[o.key].val += o.val;
}, Object.create(null));
console.log(grouped);.as-console-wrapper { max-height: 100% !important; top: 0; }Another approach is to collect all key/value pairs in a Map and format the final array with Array.from and a callback for the objects.
var array = [{ 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 }],
grouped = Array.from(
array.reduce((m, { key, val }) => m.set(key, (m.get(key) || 0) + val), new Map),
([key, val]) => ({ key, val })
);
console.log(grouped);.as-console-wrapper { max-height: 100% !important; top: 0; }