Populate array with items of another array in ascending order (Javascript)

Question

I have an array of arrays of different lengths. So for instance in my test below I start with my vidArray containing 4 arrays (their length is respectively 16, 38, 49, 49). I'd like to populate a newArray with the first value of each of the 4 arrays, then the second value of each, then the third and so on.

What I'm trying is:

      // populate newArray
      var newArray = []
      for(let i=0; i < vidArray.length; i++){
        let ar = vidArray[i]
        for(let j=i; j < (i+1); j++){
          newArray.push(ar[j])
        }
      }

      console.log("newArray "+newArray)

but it seems to wrongly take the [0] from the first array, the [1] from the second array, the [3] from the third array and so on

What will you do when there is no more items in first array, but exists in second? null/terminate? — Justinas
– Justinas, Commented Dec 27, 2020 at 23:22
So you just want to go until the end of the shortest subarray has been reached? — leisheng
– leisheng, Commented Dec 27, 2020 at 23:26

Nick · Accepted Answer · 2020-12-27 23:31:06Z

1

You can figure out the maximum length of the subarrays, then iterate over that length, pushing the corresponding values from each subarray into the new array as you go, skipping any that don't exist:

const vidArray = [
  [1, 2, 3, 4, 5],
  [11, 12, 13, 14],
  [21, 22, 23],
  [31, 32, 33, 34, 35, 36]
];

let newArray = [];
const maxLength = Math.max(...vidArray.map(a => a.length));

for (let i = 0; i < maxLength; i++) {
  vidArray.forEach(a => {
    if (a[i]) newArray.push(a[i]);
  });
}

console.log(newArray);

edited Dec 27, 2020 at 23:31

answered Dec 27, 2020 at 23:24

Nick

147k23 gold badges67 silver badges106 bronze badges

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

2 Comments

m4tt Over a year ago

It works thank you! node suggested me to declare "i" so i did: for (let i = 0; i..etc

Nick Over a year ago

@m4tt sorry, that let should be there. I've updated the answer.

Nick · Accepted Answer · 2020-12-27 23:24:47Z

0

Here is one potential method that uses a combination of reduce and forEach.

const vidArray = [
  ["a1", "a2", "a3", "a4"],
  ["b1", "b2"],
  ["c1", "c2", "c3", "c4"],
  ["d1", "d2", "d3"]
]

const newArr = vidArray.reduce((acc, arr) => {
  arr.forEach((el, i) => {
    if (!acc[i]) acc[i] = [];
    acc[i].push(el);
  });
  return acc;
}, []);

console.log(newArr);

// If you need the output as one singular array:
console.log(newArr.flat());

answered Dec 27, 2020 at 23:24

Nick

16.7k3 gold badges21 silver badges38 bronze badges

Collectives™ on Stack Overflow

Populate array with items of another array in ascending order (Javascript)

2 Answers 2

2 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

2 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related