JavaScript：创建未知维多维数组函数时的按引用传递问题

Question

I'm posting this question because I am trying to make a function that allows someone to create a multi-dim array. So, the user inputs an array of numbers which are the dimensions of the array (eg entering [2, 4, 3] would output a 2x4x3 multi-dim array) I have spent a couple of hours trying to imagine an algorithm that can do this in JS and I came up with this:

Note: I use Node.js v9.11.1

function generate(dimensions) {

  // SA = sub-array (I will use this several times here)

  // This array will store every SAs of the multi-dim array
  // E.g for a 2x4x3 array, it will store a 2-item array, a 4-item array and a 3-item array
  var arrays = []

  // This fills `arrays` with the SAs
  for (var i = 0; i < dimensions.length; i++) arrays.push(new Array(dimensions[i]).slice(0))

  // Here it gets a bit complex (at least for me!)
  // So what we do is that for each SA (except last), we fill it with copies of the current+1 SA
  // So the SA at index 1 will be filled with copies of the array at index 2
  // And the array at index 0 will be filled with arrays of index 1 (which was already filled because our for loop starts from the end)
  // The array at index 0 is our final multi-dim array

  // Goes from the before last SA to the first
  for (var current = dimensions.length-2; current !== -1; current--) {

    // Fills the current SA with index+1 SA
    for (var i = 0; i < arrays[current].length; i++) arrays[current][i] = arrays[current+1].slice(0)

  }

  // Returns first array, the complete one
  return arrays[0].slice(0)
}

My problem is that even if the array is well generated, some SA are passed by reference and not by value so when I do

my_array = generate([2, 4, 3])
my_array[1][2][1] = "hi!" // Fill a random place with "hi!"

Then when I do console.log(my_array) , some other cases of the multi-dim array are filled with the same value. This means that somewhere, an array is passed by reference rather than passed by value which is strange because I checked the code multiple times and I don't find where this could come from (I use the Array.slice() method to "copy" the array)

Have I missed something huge? Your help would be rather appreciated!

Answer 1

To be honest, not sure how your trying to create your mult-dim array,..

But the first thing that springs to mind when seeing something like this, is recursion.

eg..

 function generate(dimensions) { if (!dimensions.length) throw new Error("no dims?"); const dimsize = dimensions[0]; if (dimensions.length === 1) { return new Array(dimsize).fill(null); } const ret = []; const subdims = dimensions.slice(1); for (let l = 0; l < dimsize; l+= 1) ret.push(generate(subdims)); return ret; } const my_array = generate([2, 4, 3]) my_array[1][2][1] = "hi!" console.log(my_array); 

Answer 2

I come up with this:

 function generate(dims) { if(dims.length > 0) { let array = new Array(dims[0]).fill(0); let childDims = dims.slice(); childDims.shift(); return array.map((el) => { return generate(childDims); }); } else return 0; } let foo = generate([2, 3, 2]); foo[0][0][1] = 'hmmmm'; console.log(foo); 

Also using recursion to create multidimensional array. But when creating arrays as You saw, have to be carefull about not passing references but real copies of arrays. Slice() will give You only shallow copy.