How to copy parts of an 2d array?

Question

I'm using JavaScript in google app script and I'm super confused why there is no simple way to copy stuff by value. I just want a simple way to copy a part of my matrix values2 into the new matrix matrix1. Why is that not possible?

var temp = []; 
for (var t = 0; t<9;t++) {temp[t]= 0;}; //[0,0,0,0,0,0,0,0,0]
var matrix1 = [];
for (var x = 0; x<20;x++) {matrix1[x]=temp;};
for (var x = 0; x < 20; x++) {
  for (var y = 0; y < 9 ; y++) {
    matrix1[x][y] = values2[x+1][y+1];
}};

The code above fills the matrix with identical (last) lines.

`matrix1[x][y] = values2[x+1][y+1];` Where did you declare `values2`? — Pimmol, Jun 03 '16 at 06:54
FWIW, `Array(10).fill(0)` to produce `[0,0,0,..]`. Combine that technique with an `Array.map` to create a bunch of arrays of arrays with very little code... — deceze, Jun 03 '16 at 06:59

score 0 · Answer 1 · answered Jun 03 '16 at 07:00

Passing array as reference is common among programming languages. In this case, you don't even need temp:

var matrix1 = [];
for (var x = 0; x < 20; x++) {
  matrix1[x] = [];
  for (var y = 0; y < 9; y++) {
    matrix1[x][y] = values2[x + 1][y + 1];
  }
};

How to copy parts of an 2d array?

1 Answers1