Declare an empty two-dimensional array in Javascript?

Question

I want to create a two dimensional array in Javascript where I\'m going to store coordinates (x,y). I don\'t know yet how many pairs of coordinates I will have because they

Answer 1

What's wrong with

var arr2 = new Array(10,20);
    arr2[0,0] = 5;
    arr2[0,1] = 2
    console.log("sum is   " + (arr2[0,0] +  arr2[0,1]))

should read out "sum is 7"

Answer 2

You can just declare a regular array like so:

var arry = [];

Then when you have a pair of values to add to the array, all you need to do is:

arry.push([value_1, value2]);

And yes, the first time you call arry.push, the pair of values will be placed at index 0.

From the nodejs repl:

> var arry = [];
undefined
> arry.push([1,2]);
1
> arry
[ [ 1, 2 ] ]
> arry.push([2,3]);
2
> arry
[ [ 1, 2 ], [ 2, 3 ] ]

Of course, since javascript is dynamically typed, there will be no type checker enforcing that the array remains 2 dimensional. You will have to make sure to only add pairs of coordinates and not do the following:

> arry.push(100);
3
> arry
[ [ 1, 2 ],
  [ 2, 3 ],
  100 ]

Answer 3

You can try something like this:-

var arr = new Array([]);

Push data:

arr[0][0] = 'abc xyz';

Answer 4

We usually know the number of columns but maybe not rows (records). Here is an example of my solution making use of much of the above here. (For those here more experienced in JS than me - pretty much everone - any code improvement suggestions welcome)

     var a_cols = [null,null,null,null,null,null,null,null,null];
     var a_rxc  = [[a_cols]];

     // just checking  var arr =  a_rxc.length ; //Array.isArray(a_rxc);
     // alert ("a_rxc length=" + arr) ; Returned 1 
     /* Quick test of array to check can assign new rows to a_rxc. 
        i can be treated as the rows dimension and  j the columns*/
       for (i=0; i<3; i++) {
          for (j=0; j<9; j++) {
            a_rxc[i][j] = i*j;
            alert ("i=" + i + "j=" + j + "  "  + a_rxc[i][j] );
           }
          if (i+1<3) { a_rxc[i+1] = [[a_cols]]; }
        }

And if passing this array to the sever the ajax that works for me is

 $.post("../ajax/myservercode.php",
       {
        jqArrArg1 : a_onedimarray,
        jqArrArg2 : a_rxc
       },
       function(){  },"text" )
        .done(function(srvresp,status) { $("#id_PageContainer").html(srvresp);} ) 
        .fail(function(jqXHR,status) { alert("jqXHR AJAX error " + jqXHR + ">>" + status );} );

Answer 5

One line solution:

var x = 3, y = 4;

var ar = new Array(x).fill(new Array(y).fill(0));

It creates matrix array with values = 0

Answer 6

If you want to initialize along with the creation, you can use fill and map.

const matrix = new Array(5).fill(0).map(() => new Array(4).fill(0));

5 is the number of rows and 4 is the number of columns.