get a n-dimensions array, iterate through indexes from a specified dimension

iterateDimensionsFrom.js

/**
 * returns [1, 4, 12] from [4, 3, 2]
 * @param {number[]} array 
 */
function getArrayScale (array) {
  let scale = 1
  return array.map(dim => {
    const x = scale
    scale *= dim
    return x
  })
}

/**
 * yields [0, 0], [1, 0], [0, 1], [1, 1] from [2, 2]
 * @param {number[]} dimensions 
 */
function* iterateDimensions(dimensions) {
  let index = 0
  let max = dimensions.reduce((t, x) => t * x)
  const iterator = dimensions.map(() => 0)
  while (true) {
    yield [...iterator]
    if (++index === max) {
        break
    }
    let dimIndex = 0
    while (iterator[dimIndex] === dimensions[dimIndex] -1) {
      iterator[dimIndex] = 0
      dimIndex++
    }
    iterator[dimIndex] = iterator[dimIndex] + 1
  }
}

/**
 * Should yield over iterator (and not array) to save space.
 * @param {number[]} dimensions 
 * @param {number} dimIndex 
 */
function* iterateDimensionsFrom(dimensions, dimIndex) {
  const scales = getArrayScale(dimensions)
  const getIndex = coords => coords.reduce((t, x, i) => t + x * scales[i], 0)
  const beforeDimensions = dimensions.slice(0, dimIndex)
  const afterDimensions = dimensions.slice(dimIndex + 1)
  const otherDimensions = [...beforeDimensions, ...afterDimensions]
  const max = dimensions[dimIndex]
  for (let i = 0; i < max; i++) {
    // here, the array is cooked, but it's suboptimal
    yield [...iterateDimensions(otherDimensions)].map(coords => {
      const fullCoords = [...coords.slice(0, dimIndex), i, ...coords.slice(dimIndex)]
      return getIndex(fullCoords)
    })
  }
}



const format = a => a.map(a => a.map(n => `${n},`.padEnd(4, ' ')).join('')).join('\n')

console.log(format([...iterateDimensionsFrom([4, 3, 2], 0)]))
console.log(format([...iterateDimensionsFrom([4, 3, 2], 1)]))
console.log(format([...iterateDimensionsFrom([4, 3, 2], 2)]))

// output 

// 0,  4,  8,  12, 16, 20, 
// 1,  5,  9,  13, 17, 21, 
// 2,  6,  10, 14, 18, 22, 
// 3,  7,  11, 15, 19, 23,

// 0,  1,  2,  3,  12, 13, 14, 15, 
// 4,  5,  6,  7,  16, 17, 18, 19, 
// 8,  9,  10, 11, 20, 21, 22, 23, 

// 0,  1,  2,  3,  4,  5,  6,  7,  8,  9,  10, 11, 
// 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23,