Typescript - multidimensional array initialization

Question

I'm playing with Typescript and I wonder, how to properly instantiate and declare multidimensional array. Here's my code:

class Something {
    private things: Thing[][];

    constructor() {
        things = [][]; ??? how instantiate object ???

        for(var i: number = 0; i < 10; i++) {
            this.things[i] = new Thing[];   ??? how instantiate 1st level ???
            for(var j: number = 0; j< 10; j++) {
                this.things[i][j] = new Thing();   ??? how instantiate 2nd lvl item ???
            }
        }
    }
}

Can you give me any hint about selected places?

score 139 · Accepted Answer · edited Nov 18 '18 at 12:40

139

You only need [] to instantiate an array - this is true regardless of its type. The fact that the array is of an array type is immaterial.

The same thing applies at the first level in your loop. It is merely an array and [] is a new empty array - job done.

As for the second level, if Thing is a class then new Thing() will be just fine. Otherwise, depending on the type, you may need a factory function or other expression to create one.

class Something {
    private things: Thing[][];

    constructor() {
        this.things = [];

        for(var i: number = 0; i < 10; i++) {
            this.things[i] = [];
            for(var j: number = 0; j< 10; j++) {
                this.things[i][j] = new Thing();
            }
        }
    }
}

edited Nov 18 '18 at 12:40

Stuart Hallows

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answered May 09 '15 at 20:22

Puppy

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I can't imagine, how typings are preserved here. Can you give me any examples, please? – Fka May 09 '15 at 20:25
2

There are 0 items in the array, so there's no value or object to type. – Puppy Aug 03 '15 at 09:35
I guess, it should be `this.things = [];` in the constructor. – stefanbschneider Sep 30 '18 at 16:28

score 30 · Answer 2 · edited Jul 13 '21 at 23:23

30

Here is an example of initializing a boolean[][]:

const n = 8; // or some dynamic value
const palindrome: boolean[][] = new Array(n)
                                   .fill(false)
                                   .map(() => 
                                     new Array(n).fill(false)
                                   );

edited Jul 13 '21 at 23:23

ggorlen

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answered Mar 03 '19 at 03:02

techguy2000

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RMuesi · Answer 3 · 2017-12-14T17:50:51.180

20

If you want to do it typed:

class Something {

  areas: Area[][];

  constructor() {
    this.areas = new Array<Array<Area>>();
    for (let y = 0; y <= 100; y++) {
      let row:Area[]  = new Array<Area>();      
      for (let x = 0; x <=100; x++){
        row.push(new Area(x, y));
      }
      this.areas.push(row);
    }
  }
}

edited Dec 14 '17 at 17:50

answered Dec 13 '17 at 19:55

RMuesi

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Thanks, but not everyone is using AngularJs to write JS/TS code. – Fka Dec 14 '17 at 08:29
10

This is just standard TS code, right? What do you see as AngularJs specific? I prefer this solution with types. Thanks – What Would Be Cool Jun 27 '18 at 18:30
2

@WhatWouldBeCool the answer was edited to remove AngularJs specific code – mattumotu Nov 14 '19 at 11:15

score 8 · Answer 4 · edited Jul 08 '22 at 12:04

You can do the following (which I find trivial, but its actually correct). For anyone trying to find how to initialize a two-dimensional array in TypeScript (like myself).

Let's assume that you want to initialize a two-dimensional array, of any type. You can do the following

const myArray: any[][] = [];

And later, when you want to populate it, you can do the following:

myArray.push([<your value goes here>]);

A short example of the above can be the following:

const myArray: string[][] = []; 
myArray.push(["value1", "value2"]);

Pipo · Answer 5 · 2018-12-25T00:32:15.603

-3

Beware of the use of push method, if you don't use indexes, it won't work!

var main2dArray: Things[][] = []

main2dArray.push(someTmp1dArray)
main2dArray.push(someOtherTmp1dArray)

gives only a 1 line array!

use

main2dArray[0] = someTmp1dArray
main2dArray[1] = someOtherTmp1dArray

to get your 2d array working!!!

Other beware! foreach doesn't seem to work with 2d arrays!

edited Dec 25 '18 at 00:32

answered Dec 25 '18 at 00:25

Pipo

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Typescript - multidimensional array initialization

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