How to use Array.reduce()?

Question

I have a JSON response like below:

[
{"name": "a", "data": [{"value":10,"id":1},{"value":20,"id":2}],
{"name": "b", "data": [{"value":10,"id":1},{"value":20,"id":2}],
{"name": "c", "data": [{"value":10,"id":1},{"value":20,"id":2}],
{"name": "d", "data": [{"value":10,"id":1},{"value":20,"id":2}],
{"name": "e", "data": [{"value":10,"id":1},{"value":20,"id":2}],
]

How to sum each "value" inside each element of data (column wise) and get the result like:

[{"name": "something", "data":[{"value":50,"id":1},{"value":100,"id":2}]

How to use array.reduce() for this or is there any other method to achieve the above result?

You spec is not clear. We can understand how to reduce values by id, but your given suggested result is not clear about the "name" key... Do you want to reduce the names? — Jean-Baptiste Yunès
– Jean-Baptiste Yunès, Commented May 24, 2018 at 11:24
the final result you want is the some of values based on their id's?? so you should look for [{"value":50,"id":1},{"value":100,"id":2}] not for name. — Naresh Thakur
– Naresh Thakur, Commented May 24, 2018 at 11:30

ngChaitanya · Accepted Answer · 2018-05-24 11:42:17Z

2

Try out the following logic.

var series = [{"name": "a", "data": [{"value":10,"id":1},{"value":20,"id":2}]}, ... , ....]

var resultSeries = series.reduce((acc, cur) => {
    var result = {
        name: ‘Something’,
        data: []
    };
    var dataArray = acc.data.map((el, i) => {
        var curData = cur.data[i] || {};
        var sum = (el.value || 0) + (curData.value || 0);
        return {
            value: sum
        }
    });
    result.data = dataArray ;
    return result;
})

now resultSeries will hold

[{"name": "something", "data":[{"value":50,"id":1},{"value":100,"id":2}]

answered May 24, 2018 at 11:42

ngChaitanya

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Comments

Nina Scholz · Accepted Answer · 2018-05-24 11:32:52Z

You could take an object as hash table for the id and sum the values.

var array = [{ name: "a", data: [{ value: 10, id: 1 }, { value: 20, id: 2 }] }, { name: "b", data: [{ value: 10, id: 1 }, { value: 20, id: 2 }] }, { name: "c", data: [{ value: 10, id: 1 }, { value: 20, id: 2 }] }, { name: "d", data: [{ value: 10, id: 1 }, { value: 20, id: 2 }] }, { name: "e", data: [{ value: 10, id: 1 }, { value: 20, id: 2 }] }],
    result = { name: 'something', data: Object.values(array.reduce((r, { data }) => {
        data.forEach(({ value, id }) => {
            r[id] = r[id] || { value: 0, id };
            r[id].value += value;
        });
        return r;
    }, Object.create(null))) };

console.log(result);

.as-console-wrapper { max-height: 100% !important; top: 0; }

Dishonered · Accepted Answer · 2018-05-24 11:32:07Z

Try this code

<script>
 var numbers = [
{"name": "a", "data": [{"value":10,"id":1},{"value":20,"id":2}]},
{"name": "b", "data": [{"value":10,"id":1},{"value":20,"id":2}]},
{"name": "c", "data": [{"value":10,"id":1},{"value":20,"id":2}]},
{"name": "d", "data": [{"value":10,"id":1},{"value":20,"id":2}]},
{"name": "e", "data": [{"value":10,"id":1},{"value":20,"id":2}]},
];

function getSum(total, val) {
  total.data[0].value = total.data[0].value + val.data[0].value;
  total.data[1].value = total.data[1].value + val.data[1].value;
  return total;
 }
function myFunction(item) {
   document.getElementById("demo").innerHTML = 
  JSON.stringify(numbers.reduce(getSum));
}

This prints

Sum of numbers in array: {"name":"a","data":[{"value":50,"id":1},{"value":100,"id":2}]}

The code just adds the values on each iteration and updates the existing value.

Nikhil Aggarwal · Accepted Answer · 2018-05-24 11:41:11Z

0

Use Array.reduce and Array.map

var arr =[{"name": "a", "data": [{"value":10,"id":1},{"value":20,"id":2}]},{"name": "b", "data": [{"value":10,"id":1},{"value":20,"id":2}]},{"name": "c", "data": [{"value":10,"id":1},{"value":20,"id":2}]},{"name": "d", "data": [{"value":10,"id":1},{"value":20,"id":2}]},{"name": "e", "data": [{"value":10,"id":1},{"value":20,"id":2}]}];

var result = {
   "name" : "something",
   "data" : arr.reduce((a,c) => { // reduces/merges 2 records of arr
      a.data.map((v, i) => { // add values for the 2 records (column wise)
        v.value = v.value + c.data[i].value;
        return v;
      });
      return a;
   })
};
console.log(result);

edited May 24, 2018 at 11:41

answered May 24, 2018 at 11:34

Nikhil Aggarwal

28.5k4 gold badges46 silver badges61 bronze badges

Comments

Ramya Ramanathan · Accepted Answer · 2018-05-24 11:51:03Z

I believe your JSON data looks like what I've used in the below snippet. You could do this:

    a = [
    {"name": "a", "data": [{"value":10,"id":1},{"value":20,"id":2}]},
    {"name": "b", "data": [{"value":10,"id":1},{"value":20,"id":2}]},
    {"name": "c", "data": [{"value":10,"id":1},{"value":20,"id":2}]},
    {"name": "d", "data": [{"value":10,"id":1},{"value":20,"id":2}]},
    {"name": "e", "data": [{"value":10,"id":1},{"value":20,"id":2}]},
    ]
    
    let reducer = (accumulator, currValue) => {
            accumulator.name = "something";
        	for (let i = 0; i < accumulator.data.length; i++) {
        			accumulator.data[i].value += currValue.data[i].value;
            }
            return accumulator
        };

    // This will give the result you want:

    console.log(a.reduce(reducer));

The result will be:

{"name":"something","data":[{"value":50,"id":1},{"value":100,"id":2}]}

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