caleb15 caleb15 - 3 months ago 15
Javascript Question

Creating 2d-array from 1d array

Im new to programming, I have an assignment that asks to create a 2d-array from a 1d array. I came up with this (no help from any outside sources because it takes away the learning experience). It works for our professors test inputs, I was just wondering is this an ugly/inefficient solution.

function twoDArray(arr, lenSubArray) {
var newArr = [];
var placeHolder = 0;
var leftOver = 0;
for (var i = 1; i < arr.length + 1; i++) {
/* if i is a multiple of the specified sub-array size
then add the elements from placeHolder to i
*/
if (i % lenSubArray === 0) {
newArr.push(arr.slice(placeHolder, i));
placeHolder += lenSubArray;
leftOver++; // tells us how many sub-arrays were created
}
}
/* if original array is not divisible by the length of the specified sub-array
then there will be left over values. Retrieve these values and create an
array out of them and add them to the 2d array.
*/
if (!(arr.length % lenSubArray === 0)) {
/* sub-array count multiplied by the length of each
sub-array gives us the right index to retrieve remaining values
*/
leftOver = (leftOver * lenSubArray);
newArr.push(arr.slice(leftOver))
}

return newArr;
}


Test input: twoDArray([1, 2, 3, 4, 5], 3)
output would be: [[1, 2, 3], [4, 5]]

Answer

you're way too complicated:

  • create a result-array
  • push slices from i to i+lenSubArray
  • increment i by lenSubArray

and slice is smart enough to properly handle the end of the Array

function twoDArray(arr, lenSubArray) {
  var i = 0, result = [];
  while(i < arr.length)
    result.push( arr.slice(i, i+=lenSubArray) );
  return result;  
}