How to merge multiple arrays in foreach loop in Javascript

Question

How to merge multiple arrays in foreach loop. I'm trying to merge all 3 imageData arrays in one single array. Please tell if I missed anything from following method.

  const imageArray = [
      {
        imageData: [
          'https://via.placeholder.com/50',
          'https://via.placeholder.com/60'
        ],
      },
      {
        imageData: [
          'https://via.placeholder.com/100'
        ],
      },
      {
        imageData: [
          'https://via.placeholder.com/150'
        ],
     }
  ];

  processImage() {
    imageArray.forEach((element) => {
      const imageCollection = [...element.imageData];
      console.log(imageCollection);
      // Expected result 
      //['https://via.placeholder.com/50', 'https://via.placeholder.com/60', 'https://via.placeholder.com/100', https://via.placeholder.com/150]
    });
  }

imageArray.reduce((p, c) => p.concat(c.imageData), []);, readable O(n²) solution for not overly large datasets. — ASDFGerte
– ASDFGerte, Commented Mar 8, 2021 at 17:19
Ngl even though it was not ES6 only (flatMap came later), i liked that solution the most, because it was very readable, and hopefully O(n) (i'd assume engines optimize that much). My glass ball tells me, that being overly specific on ES6 is not the intention anyways. — ASDFGerte
– ASDFGerte, Commented Mar 8, 2021 at 17:28
I certainly didn't mean to have @Barmar delete his answer; I actually upvoted it. I think that people are too quick to tag things with ES versions. Unless you're asking a question about the version, or want answers to only use a specific version, there's no reason to tag a question with a version. — Heretic Monkey
– Heretic Monkey, Commented Mar 8, 2021 at 17:36

zergski · Accepted Answer · 2021-03-08 17:22:06Z

6

You declare the new imageCollection inside the loop.. Thus you create a new array each iteration...

Do it outside and use imageCollection.push(...element.imageData) inside forEach loop

edited Mar 8, 2021 at 17:22

answered Mar 8, 2021 at 17:20

zergski

8454 silver badges10 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

zergski Over a year ago

right sorry forgot the spread operator. Edited answere

Alyson Maia · Accepted Answer · 2021-03-09 08:05:12Z

5

Your array needs to be outside the forEach loop so it is accessible after the forEach is completed.

const imageArray = [
  {
    imageData: [
      'https://via.placeholder.com/50',
      'https://via.placeholder.com/60'
    ]
  },
  {
    imageData: ['https://via.placeholder.com/100']
  },
  {
    imageData: ['https://via.placeholder.com/150']
  }
];

const processImage = function (imageArray) {
  const imageCollection = [];
  imageArray.forEach(element => {
    imageCollection.push(...element.imageData);
  });
  return imageCollection;
};

Expected result for processImage(imageArray)

[
  'https://via.placeholder.com/50',
  'https://via.placeholder.com/60',
  'https://via.placeholder.com/100',
  'https://via.placeholder.com/150'
]

edited Mar 9, 2021 at 8:05

Alyson Maia

8105 silver badges14 bronze badges

answered Mar 8, 2021 at 17:41

Josh McCormick

511 bronze badge

Comments

Omar Shishani · Accepted Answer · 2021-03-08 19:24:48Z

You can assign imageCollection outside of the forEach (but still inside of processImage()). Then in the redefinition of imageCollection inside of the forEach, spread the contents of each previous imageCollection array, followed by the contents of element.imageData. Like so:

//...
processImage() {
  let imageCollection = [];
  imageArray.forEach((element) => {
    imageCollection = [...imageCollection, ...element.imageData];
//...

Full Code for Your Context

const imageArray = [
    {
      imageData: [
        'https://via.placeholder.com/50',
        'https://via.placeholder.com/60'
      ],
    },
    {
      imageData: [
        'https://via.placeholder.com/100'
      ],
    },
    {
      imageData: [
        'https://via.placeholder.com/150'
      ],
    }
];

processImage() {
  let imageCollection = [];
  imageArray.forEach((element) => {
    imageCollection = [...imageCollection, ...element.imageData];
    console.log(imageCollection);
    // Expected result 
    //['https://via.placeholder.com/50', 'https://via.placeholder.com/60', 'https://via.placeholder.com/100', https://via.placeholder.com/150]
  });
  console.log('ImageCollection',imageCollection);
}

Full Code for Running Outside of Your Context

const imageArray = [
    {
      imageData: [
        'https://via.placeholder.com/50',
        'https://via.placeholder.com/60'
      ],
    },
    {
      imageData: [
        'https://via.placeholder.com/100'
      ],
    },
    {
      imageData: [
        'https://via.placeholder.com/150'
      ],
    }
];

function processImage() {
  let imageCollection = [];
  imageArray.forEach((element) => {
    imageCollection = [...imageCollection, ...element.imageData];
    console.log(imageCollection);
    // Expected result 
    //['https://via.placeholder.com/50', 'https://via.placeholder.com/60', 'https://via.placeholder.com/100', https://via.placeholder.com/150]
  });
  console.log('ImageCollect',imageCollection);
}

processImage();

nativelectronic · Accepted Answer · 2021-03-08 17:59:18Z

0

try this,foreach in the object imageData, and saving each value in an array using another Foreach.

    let newImageData = []

    imageArray.forEach((data)=>{

       const imageDataArray = data.imageData
       imageDataArray.forEach(link => {
        newImageData.push(link)
       });
      

  })
  
  const NewImageArray = {imageData:newImageData}
  console.log(NewImageArray)

edited Mar 8, 2021 at 17:59

answered Mar 8, 2021 at 17:38

nativelectronic

8928 silver badges11 bronze badges

2 Comments

zergski Over a year ago

Why use both map and forEach when the task can be accomplished with one of them? Additionally you did not define a return statement in your map. This will yield an error.

nativelectronic Over a year ago

i was mapping without create a new object with the return, but u are right, better a simple foreach instead. is a aproach, i think is most readable

Collectives™ on Stack Overflow

How to merge multiple arrays in foreach loop in Javascript

4 Answers 4

1 Comment

Comments

Full Code for Your Context

Full Code for Running Outside of Your Context

Comments

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

1 Comment

Comments

Full Code for Your Context

Full Code for Running Outside of Your Context

Comments

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related