Sum all data in array of objects into new array of objects

Question

I have an array of objects that looks like this:

var data = [     { costOfAirtickets: 2500, costOfHotel: 1200 },     { costOfAirtickets: 1500, costOfHotel: 1000 }, ] 

and I want to sum each element in the array to produce an array like this:

var result = [ { costOfAirtickets: 4000, costOfHotel: 2200 } ] 

I have used a map and reduce function but I was able to only sum an individual element like so:

data.map(item => item.costOfAirtickets).reduce((prev, next) => prev + next); // 22 

At the moment this produces a single value which is not what I want as per initial explanation.

Is there a way to do this in Javascript or probably with lodash.

Answer 1

Using for..in to iterate object and reduce to iterate array

var data = [{costOfAirtickets: 2500, costOfHotel: 1200},{costOfAirtickets: 1500, costOfHotel: 1000}];    var result = [data.reduce((acc, n) => {    for (var prop in n) {      if (acc.hasOwnProperty(prop)) acc[prop] += n[prop];      else acc[prop] = n[prop];    }    return acc;  }, {})]  console.log(result)

Answer 2

Use Lodash to simplify your life.

const _ = require('lodash') let keys = ['costOfAirtickets', 'costOfHotel'];  let results = _.zipObject(keys, keys.map(key => _.sum( _.map(data, key)))) ... { costOfAirtickets: 4000, costOfHotel: 2200 } 

Explanation:

• _.sum(_.map(data, key)): generates sum of each array
• _.zipObject: zips the results with the array sum
• using keys.map() for sum of each key as _.map does not guarantee order.

Documentation:

• sum: https://lodash.com/docs/4.17.10#sum
• zipObject: https://lodash.com/docs/4.17.10#zipObject
• map: https://lodash.com/docs/4.17.10#map