Merge arrays from object property in an object array [closed]

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Give an array of objects as below:

var objArray = [{'key': 'key1', 'fields': [1, 2]}, {'key': 'key2', 'fields': [3, 4]}];

I would like to get an array of merged items from fields property and output should be 1, 2, 3, 4

I've tried to merge as below. I'm not satisfied with my solution and would like to get feedback's and improve upon my solution. I'm new to JS and typescript. I believe there is better solution with features of ES6. Can someone help to improve my solution?

function mergeArraysFromObjectArray(objArray){
   let allFields = [];
    for (let obj of objArray) {
      for (let propt in obj) {
        if (obj.hasOwnProperty(propt) && propt === 'fields') {
          allFields = allFields.concat(obj[propt]);
        }
      }
    } 

  return allFields;
}

var objArray = [{'key': 'key1', 'fields': [1, 2]}, {'key': 'key2', 'fields': [3, 4]}];
let allMergedFields = mergeArraysFromObjectArray(objArray);

for(let i=0; i < allMergedFields.length; i++){
   console.log(allMergedFields[i]);  //prints - 1, 2, 3, 4
}

For working code that you want reviewed, see codereview.stackexchange.com — Matt D. Webb
– Matt D. Webb, Commented Aug 30, 2017 at 12:24
I'm voting to close this question as off-topic because it's better suited to codereview.stackexchange.com — Matt S
– Matt S, Commented Aug 30, 2017 at 15:45
The question that was suggested as off-topic should be moved to codereview.stackexchange.com, not closed as Opinion-based. — Michael Freidgeim
– Michael Freidgeim, Commented Sep 21, 2020 at 3:28

Yosvel Quintero · Accepted Answer · 2022-11-23 10:06:28Z

11

You can use Array.prototype.flatMap()

Code example 1:

const objArray = [{key: 'key1', fields: [1, 2]}, {key: 'key2', fields: [3, 4]}]
const result = objArray.flatMap(({ fields }) => fields)

console.log(result)

Also you can use Array.prototype.map() and Array.prototype.flat()

Code example 2:

const objArray = [{key: 'key1', fields: [1, 2]}, {key: 'key2', fields: [3, 4]}]
const result = objArray.map(({ fields }) => fields).flat()

console.log(result)

Also you can use Array.prototye.reduce() combined with destructuring assignment and spread syntax

Code example 3:

const objArray = [{key: 'key1', fields: [1, 2]}, {key: 'key2', fields: [3, 4]}]
const result = objArray.reduce((a, { fields }) => [...a, ...fields], [])

console.log(result)

Also using just Array.prototye.reduce() combined with Array.prototype.concat():

Code example 4:

const objArray = [{key: 'key1', fields: [1, 2]}, {key: 'key2', fields: [3, 4]}]
const result = objArray.reduce((a, { fields }) => a.concat(fields), [])

console.log(result)

edited Nov 23, 2022 at 10:06

answered Aug 30, 2017 at 12:33

Yosvel Quintero

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1 Comment

Nenad Kaevik Over a year ago

This is how you do it properly :) Es6 baby :) Good job

Ankit Agarwal · Accepted Answer · 2017-08-30 12:24:08Z

5

You can simply concat the array and create a new array inside a loop:

var objArray = [{'key': 'key1', 'fields': [1, 2]}, {'key': 'key2', 'fields': [3, 4]}];

var result = [];
for(var i=0; i<objArray.length; i++){
   result = result.concat(objArray[i].fields);
}

console.log(result);

answered Aug 30, 2017 at 12:24

Ankit Agarwal

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Comments

Nenad Vracar · Accepted Answer · 2017-08-30 12:31:25Z

3

You can use spread syntax ... and map() to get fields property

var objArray = [{'key': 'key1', 'fields': [1, 2]}, {'key': 'key2', 'fields': [3, 4]}];
var result = [].concat(...objArray.map(({fields}) => fields))
console.log(result)

You can also add filter(Boolean) to remove undefined in case there is no fields property.

var objArray = [{'key': 'key1', 'asdf': [1, 2]}, {'key': 'key2', 'fields': [3, 4]}];
var result = [].concat(...objArray.map(e => e.fields).filter(Boolean))
console.log(result)

edited Aug 30, 2017 at 12:31

answered Aug 30, 2017 at 12:24

Nenad Vracar

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