How to add a key value pair to an array in Javascript / Jquery

Question

I have 2 arrays as below

var dataSource = [
{location: "France", January: 79, February: 81, March: 23},  
{location: "Germany", January: 98, February: 83},
{location: "Japan", January: 96, March: 11} ];

var Months = ["January","February","March"];

I want to loop through each object in dataSource and check if all values of Months exist in each objects of dataSource. If the value doesn't exist in dataSource then add that value to dataSource with value = 100

example : in location Germany, the month "March" does not exist so I need to push the key and value March : 100

at the end dataSource should be as below

var dataSource = [
{location: "France", January: 79, February: 81, March: 23},  
{location: "Germany", January: 98, February: 83, March: 100},
{location: "Japan", January: 96, February: 100, March: 11} ];

I tried many solutions from previous threads but I am not getting the exact result I want. Here are some of my ideas

var dataSource = [
{location: "France", January: 79, February: 81, March: 23},  
{location: "Germany", January: 98, February: 83},
{location: "Japan", January: 96, March: 11} ];

var Months = ["January","February","March"];

dataSource.forEach(function(element) {
Months.forEach(function(item) {
  if (!(item in element)) {
//Object.assign(dataSource, {item: 100}); 
//dataSource = {...dataSource, ...{item: 100}}
dataSource.push({item: 100});
  }
});
});

console.log(dataSource);

Thank you for your suggestions.

Ori Drori · Accepted Answer · 2019-03-07 18:40:47Z

6

You can use Array.map() to iterate the dataSource array. Use an internal Array.reduce() to iterate the Months, and add missing months to the current object:

const dataSource = [{"location":"France","January":79,"February":81,"March":23},{"location":"Germany","January":98,"February":83},{"location":"Japan","January":96,"March":11}];
const Months = ["January","February","March"];

const result = dataSource.map(o =>
  Months.reduce((obj, m) => m in obj ? obj : { ...obj, [m]: 100 }, o)
);

console.log(result);

answered Mar 7, 2019 at 18:40

Ori Drori

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Taplar · Accepted Answer · 2019-03-07 18:47:36Z

2

You can loop through the sources and months, setting the months on the sources as the value they already have, or defaulting to 100.

var dataSource = [{
    location: "France",
    January: 79,
    February: 81,
    March: 23
  },
  {
    location: "Germany",
    January: 98,
    February: 83
  },
  {
    location: "Japan",
    January: 96,
    March: 11
  }
];

var Months = ["January", "February", "March"];

dataSource.forEach(function(element){
  Months.forEach(function(month){
    if (element[month] === undefined) element[month] = 100;
  });
});

console.log(dataSource);

edited Mar 7, 2019 at 18:47

answered Mar 7, 2019 at 18:42

Taplar

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2 Comments

Barmar Over a year ago

This will change an explicit 0 to 100.

Taplar Over a year ago

@Barmar nice catch, fixed.

Koushik Chatterjee · Accepted Answer · 2019-03-08 09:12:37Z

Or else, you can create a hash with resultant months and their values, which you can be directly used, by assigning each object of your array on top of it. So you can process N number of inputs (arrays) with the same hash.

Example of Resultant Hash: {January: 100, February: 100, March: 100}

And then you can do this N number of time:

dataSource1.map(d => ({...hash, ...d}));
dataSource2.map(d => ({...hash, ...d}));
dataSource3.map(d => ({...hash, ...d}));

Here is the example:

let dataSource = [{"location":"France","January":79,"February":81,"March":23},{"location":"Germany","January":98,"February":83},{"location":"Japan","January":96,"March":11}],
    Months = ["January","February","March"],
    hash = Months.reduce((r, e) => ({...r, [e]: 100}), {}),
    res = dataSource.map(d => ({...hash, ...d}));
    
console.log('This is your hash: ', hash); //This is the hash generated one time
console.log('This is your result: ', res); //this is the result against that input

Coty Embry · Accepted Answer · 2019-03-07 18:54:42Z

Maybe this can help you some. Just run test() in the developer tools or something and look at the console.log output

pay attention to the uniqueKeys object since its where the main logic is centered around and the hasOwnProperty stuff

function test() {

    var uniqueKeys = {location: ''};                        //default to have location set
    var Months = ['January', 'February', 'March'];

    for (var i = 0; i < Months.length; i++) {
        uniqueKeys[Months[i]] = '';                     //just populate the object from the array to use soon
    }


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




        var validObject = true;
        Object.keys(uniqueKeys).forEach((e,j) => {

            if (dataSource[i].hasOwnProperty(e) === false) {
                validObject = false;
            }

        });

        if (validObject === false) {

            console.log('add to', dataSource[i], 'to balance it out');

        }
    }
}

hope it helps some ~cheers

r_batra · Accepted Answer · 2019-03-15 15:13:49Z

0

May be this short solution that iterates over the months and checks whether that month is present in each record for datasource. If not then add default value, 100 in your case

for(i=0;i<dataSource.length;i++){
        for(j=0;j<Months.length;j++){
            if(Months[j] in dataSource[i]){
            }
            else{
                dataSource[i][Months[j]] = 100;
            }   
        }
    }

answered Mar 15, 2019 at 15:13

r_batra

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