How to modify value of n dimensional array element where indices are specified by an array in Javascript

Question

I have an n-dimensional array and I want to access/modify an element in it using another array to specify the indices.

I figured out how to access a value, however I do not know how to modify the original value.

// Arbitrary values and shape
arr = [[[8, 5, 8],
        [9, 9, 9],
        [0, 0, 1]],

       [[7, 8, 2],
        [9, 8, 3],
        [9, 5, 6]]];

// Arbitrary values and length
index = [1, 2, 0];

// The following finds the value of arr[1][2][0]
// Where [1][2][0] is specified by the array "index"

tmp=arr.concat();

for(i = 0; i < index.length - 1; i++){
  tmp = tmp[index[i]];
}

// The correct result of 9 is returned
result = tmp[index[index.length - 1]];

How can I modify a value in the array?
Is there a better/more efficient way to access a value?

GalAbra · Accepted Answer · 2020-04-17 05:13:26Z

This is a classic recursive algorithm, as each step includes the same algorithm:

Pop the first index from indices.
Keep going with the array that the newly-popped index points to.

Until you get to the last element in indices - then replace the relevant element in the lowest-level array.

function getUpdatedArray(inputArray, indices, valueToReplace) {
  const ans = [...inputArray];
  const nextIndices = [...indices];
  const currIndex = nextIndices.shift();
  let newValue = valueToReplace;

  if (nextIndices.length > 0) {
    newValue = getUpdatedArray(
      inputArray[currIndex],
      nextIndices,
      valueToReplace,
    );
  } else if (Array.isArray(inputArray[currIndex])) {
    throw new Error('Indices array points an array');
  }

  ans.splice(currIndex, 1, newValue);
  return ans;
}

const arr = [
  [
    [8, 5, 8],
    [9, 9, 9],
    [0, 0, 1]
  ],

  [
    [7, 8, 2],
    [9, 8, 3],
    [9, 5, 6]
  ]
];
const indices = [1, 2, 0];
const newArr = getUpdatedArray(arr, indices, 100)
console.log(newArr);

Kavidu Aloka Kodikara · Accepted Answer · 2020-04-17 04:07:44Z

1

You can change the values in array like this,

arr[x][y][z] = value;

Does this help?

answered Apr 17, 2020 at 4:07

Kavidu Aloka Kodikara

3295 silver badges22 bronze badges

4 Comments

Thoughtyness Over a year ago

No. I know how to do that. My problem is doing that, only where x,y,z are specified using another array, index=[x,y,z].

Kavidu Aloka Kodikara Over a year ago

You can do like this if you can be sure that the 3rd inner array length is 3 arr[index[0]][index[1]][index[2]] = value;

Thoughtyness Over a year ago

That would work, except I need it to work for any length.

Kavidu Aloka Kodikara Over a year ago

@GalAbra has given the perfect answer I guess

NickChris · Accepted Answer · 2020-04-17 04:19:00Z

0

I think what you're looking for is this:

arr[index[0]][index[1]][index[2]] = value;

I'm having trouble understanding what you're attempting to do in the second part of your example.

answered Apr 17, 2020 at 4:19

NickChris

715 bronze badges

1 Comment

Thoughtyness Over a year ago

That's what I'm looking for, except, I need to it work for n dimensions.

Collectives™ on Stack Overflow

How to modify value of n dimensional array element where indices are specified by an array in Javascript

3 Answers 3

Comments

4 Comments

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

Comments

4 Comments

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related