JavaScript - merge two arrays of objects and de-duplicate based on property value

Question

I want to update (replace) the objects in my array with the objects in another array. Each object has the same structure. e.g.

var origArr = [
          


        

Answer 1

const origArr = [
  {name: 'Trump', isRunning: true},
  {name: 'Cruz', isRunning: true},
  {name: 'Kasich', isRunning: true}
];

const updatingArr = [
  {name: 'Cruz', isRunning: false},
  {name: 'Kasich', isRunning: false}
];

let hash = {};

for(let i of origArr.concat(updatingArr)) {
  if(!hash[i]) {
    hash[i.name] = i;
  }
}

let newArr = [];

for(let i in hash) {
  newArr.push(hash[i])
}

console.log(newArr);

Answer 2

You can use a hash which gives the index by name, and Object.assign to update.

var hash = origArr.reduce(function(hash, obj, index) {
  hash[obj.name] = index;
  return hash;
}, Object.create(null));
for(var obj of updatingArr) {
  Object.assign(origArr[hash[obj.name]], obj);
}

Answer 3

Try this approach with ES-6 Set Data Structure: const result = [...new Set([...origArr, ...updatingArr])]

Answer 4

I came here looking for exactly this, saw @Gruff Bunny 's technique and wondered if 'lodash' wouldn't perhaps be a superior option even to 'underscore'?

Lo and behold :

let result = _.unionBy(updatingArr, origArr, 'name');

Answer 5

You can give this a try.

var origArr = [
  {name: 'Trump', isRunning: true},
  {name: 'Cruz', isRunning: true},
  {name: 'Kasich', isRunning: true}
];
var updatingArr = [
  {name: 'Cruz', isRunning: false},
  {name: 'Kasich', isRunning: false}
];

var origLength = origArr.length;
var updatingLength = updatingArr.length;

//Traverse the original array and replace only if the second array also has the same value
for(i = origLength-1; i >= 0; i--) {
    for(j = updatingLength -1; j >= 0; j--) {
    if(origArr[i].name === updatingArr[j].name) {
        origArr[i] = updatingArr[j];
    }
  }
}

console.log(origArr);

Answer 6

You could use Array#map in combination with Array#reduce

var origArr = [{ name: 'Trump', isRunning: true }, { name: 'Cruz', isRunning: true }, { name: 'Kasich', isRunning: true }],
    updatingArr = [{ name: 'Cruz', isRunning: false }, { name: 'Kasich', isRunning: false }],
    NEWArr = origArr.map(function (a) {
        return this[a.name] || a;
    }, updatingArr.reduce(function (r, a) {
        r[a.name] = a;
        return r;
    }, Object.create(null)));

document.write('<pre>' + JSON.stringify(NEWArr, 0, 4) + '</pre>');