Convert a 1D array to 2D array

Question

I am working on a program where I have to read the values from a textfile into an 1D array.I have been succesfull in getting the numbers in that 1D array.

m1=[1,2,3,4,5,6,7,8,9]

but I want the array to be

m1=[[1,2,3],[4,5,6],[7,8,9]]

Answer 1

You can use this code :

const arr = [1,2,3,4,5,6,7,8,9];
    
const newArr = [];
while(arr.length) newArr.push(arr.splice(0,3));
    
console.log(newArr);

http://jsfiddle.net/JbL3p/

Answer 2

Array.prototype.reshape = function(rows, cols) {
  var copy = this.slice(0); // Copy all elements.
  this.length = 0; // Clear out existing array.

  for (var r = 0; r < rows; r++) {
    var row = [];
    for (var c = 0; c < cols; c++) {
      var i = r * cols + c;
      if (i < copy.length) {
        row.push(copy[i]);
      }
    }
    this.push(row);
  }
};

m1 = [1, 2, 3, 4, 5, 6, 7, 8, 9];

m1.reshape(3, 3); // Reshape array in-place.

console.log(m1);

.as-console-wrapper { top:0; max-height:100% !important; }

Output:

[
  [1, 2, 3],
  [4, 5, 6],
  [7, 8, 9]
]

JSFiddle DEMO

Answer 3

I suppose you could do something like this... Just iterate over the array in chunks.

m1=[1,2,3,4,5,6,7,8,9];

// array = input array
// part = size of the chunk
function splitArray(array, part) {
    var tmp = [];
    for(var i = 0; i < array.length; i += part) {
        tmp.push(array.slice(i, i + part));
    }
    return tmp;
}

console.log(splitArray(m1, 3)); // [ [ 1, 2, 3 ], [ 4, 5, 6 ], [ 7, 8, 9 ] ]

Obviously there is no error checking, but you can easily add that.

DEMO

Answer 4

There are so many ways to do the same thing:

var m = [1, 2, 3, 4, 5, 6, 7, 8, 9];
var n = [];
var i = 0;
for (l = m.length + 1; (i + 3) < l; i += 3) {
    n.push(m.slice(i, i + 3));
}
// n will be the new array with the subarrays

The above is just one.