I have two array object(arrayList1,arrayList2). Just I am trying to merge those two arrays into one array object. The following terms I used.

• Both array merged into one array based on key-name is type.
• arrayList2 values will be overwrite the arrayList1.
• I Got the expected output but I am worying to do with efficient and performance way..

Can someone please simplify my code..

Note :

• It would be great if using Array.reduce function and without use any plugin/library..
• I added the smaple input for understanding. The element order will be change and size of both array's will change.

const arrayList1 = [
    { type: "A", any: 11, other: "ab", props: "1" },
    { type: "B", any: 22, other: "bc", props: "2" }, // same type
    { type: "C", any: 33, other: "df", props: "3" }
];
 
const arrayList2 = [
    { type: "D", any: 44, other: "aa", props: "11" },
    { type: "B", any: 22, other: "bb", props: "2----2" , x: 10}, // same type
    { type: "E", any: 44, other: "cc", props: "33" }
];

result = arrayList2.reduce(function (arr1, arr2) {
  let isMatchFound = false;
  arr1.forEach(function (list) {
    if (arr2.type == list.type) {
      list = Object.assign(list, arr2);
      isMatchFound = true;
    }
  });
  if (!isMatchFound) {
    arr1.push(arr2);
  }
  return arr1;
}, arrayList1);

console.log('result', JSON.stringify(result));

I have two array object(arrayList1,arrayList2). Just I am trying to merge those two arrays into one array object. The following terms I used.

• Both array merged into one array based on key-name is type.
• arrayList2 values will be overwrite the arrayList1.
• I Got the expected output but I am worying to do with efficient and performance way..

Can someone please simplify my code..

Note :

• It would be great if using Array.reduce function and without use any plugin/library..
• I added the smaple input for understanding. The element order will be change and size of both array's will change.

const arrayList1 = [
    { type: "A", any: 11, other: "ab", props: "1" },
    { type: "B", any: 22, other: "bc", props: "2" }, // same type
    { type: "C", any: 33, other: "df", props: "3" }
];
 
const arrayList2 = [
    { type: "D", any: 44, other: "aa", props: "11" },
    { type: "B", any: 22, other: "bb", props: "2----2" , x: 10}, // same type
    { type: "E", any: 44, other: "cc", props: "33" }
];

result = arrayList2.reduce(function (arr1, arr2) {
  let isMatchFound = false;
  arr1.forEach(function (list) {
    if (arr2.type == list.type) {
      list = Object.assign(list, arr2);
      isMatchFound = true;
    }
  });
  if (!isMatchFound) {
    arr1.push(arr2);
  }
  return arr1;
}, arrayList1);

console.log('result', JSON.stringify(result));

• javascript
• arrays
• node.js
• object

• What do you want the output to be? What should result be? – Jack Bashford Commented Jan 23, 2019 at 7:01
• What is the use case here. What is the typical size of list 1 and list 2? Are they always equal? I won't be too worried about performance until it is a problem. When the codebase is huge, bottlenecks are often some where else. Machine can deal with loops etc pretty efficiently these days. – Samuel Toh Commented Jan 23, 2019 at 7:01
• @JackBashford - I got the expected output. Just want to reduce the code with efficient and performance way. – RSKMR Commented Jan 23, 2019 at 7:03
• @SamuelToh, The size of 'list-1' and 'list-2' will be change.. Mostly the format of list1, list2 will be differ. Just I added smaple json for understanding... – RSKMR Commented Jan 23, 2019 at 7:05
• @RSKMR Is ordering of elements fixed i.e. first elements of arrayList1 and then arrayList2? – Ashish Commented Jan 23, 2019 at 7:05

4 Answers 4

You may also use .reduce() and Object.values() methods to get the desired output:

const arrayList1 = [
    { type: "A", any: 11, other: "ab", props: "1" },
    { type: "B", any: 22, other: "bc", props: "2" }, // same type
    { type: "C", any: 33, other: "df", props: "3" }
];
 
const arrayList2 = [
    { type: "D", any: 44, other: "aa", props: "11" },
    { type: "B", any: 22, other: "bb", props: "2----2" , x: 10}, // same type
    { type: "E", any: 44, other: "cc", props: "33" }
];

const result = Object.values(
   [].concat(arrayList1, arrayList2)
     .reduce((r, c) => (r[c.type] = Object.assign((r[c.type] || {}), c), r), {})
);
                 
console.log(result);

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

You could do something like this using reduce and Object.values

const array1 = [
    { type: "A", any: 11, other: "ab", props: "1" },
    { type: "B", any: 22, other: "bc", props: "2" }, // same type
    { type: "C", any: 33, other: "df", props: "3" }
];
 
const array2 = [
    { type: "D", any: 44, other: "aa", props: "11" },
    { type: "B", any: 22, other: "bb", props: "2----2" , x: 10}, // same type
    { type: "E", any: 44, other: "cc", props: "33" }
];

const mapped = array1.reduce((a,t)=> (a[t.type] = t, a), {}),
      mapped2 = array2.reduce((a,t)=> (a[t.type] = t, a), {})

console.log(Object.values({...mapped, ...mapped2}))

If you just wanted to make your code smaller:

const arrayList1 = [
    { type: "A", any: 11, other: "ab", props: "1" },
    { type: "B", any: 22, other: "bc", props: "2" }, // same type
    { type: "C", any: 33, other: "df", props: "3" }
];
 
const arrayList2 = [
    { type: "D", any: 44, other: "aa", props: "11" },
    { type: "B", any: 22, other: "bb", props: "2----2" , x: 10}, // same type
    { type: "E", any: 44, other: "cc", props: "33" }
];

result = arrayList2.reduce(function(arr1, arr2) {
  if (arr1.find(({ type }) => type == arr2.type)) {
    arr1[arr1.indexOf(arr1.find(({ type }) => type == arr2.type))] = Object.assign(arr1.find(({ type }) => type == arr2.type), arr2);
    arr1.push(arr2);
  }
  return arr1;
}, arrayList1);

console.log('result', JSON.stringify(result));

If you dont exactly need arrayList1 before arrayList2, you can use this one liner simple approach. What I have done is I have destructured all elements arrayList2 and only those elements of arrayList1 whose key does not exist in arrayList1.

P.S. the problem with reduce is you have to reduce the largest array otherwise you will miss out the elements of bigger Array.

const arrayList1 = [
    { type: "A", any: 11, other: "ab", props: "1" },
    { type: "B", any: 22, other: "bc", props: "2" }, // same type
    { type: "C", any: 33, other: "df", props: "3" }
];
 
const arrayList2 = [
    { type: "D", any: 44, other: "aa", props: "11" },
    { type: "B", any: 22, other: "bb", props: "2----2" , x: 10}, // same type
    { type: "E", any: 44, other: "cc", props: "33" }
];
const output = [...arrayList2, ...arrayList1.filter(el1 => !arrayList2.some(el2 => el2.type === el1.type))]
//[].concat(arrayList2, arrayList1.filter(el1 => !arrayList2.some(el2 => el2.type === el1.type)))

console.log(output)