1411

I have been reading online and some places say it isn't possible, some say it is and then give an example and others refute the example, etc.

  1. How do I declare a 2 dimensional array in JavaScript? (assuming it's possible)

  2. How would I access its members? (myArray[0][1] or myArray[0,1]?)

12
  • 28
    Assuming a somewhat pedantic definition, it is technically impossible to create a 2d array in javascript. But you can create an array of arrays, which is tantamount to the same. Commented Jul 29, 2014 at 5:05
  • 24
    FYI... when you fill an array with more arrays using var arr2D = new Array(5).fill(new Array(3));, each element of Array(5) will point to the same Array(3). So it's best to use a for loop to dynamically populate sub arrays. Commented May 23, 2016 at 8:51
  • 95
    a = Array(5).fill(0).map(x => Array(10).fill(0)) Commented Mar 25, 2017 at 14:21
  • 5
    In other words, fill doesn't call new Array(3) for each index of the array being filled, since it's not a lambda expression or anything, such as Longfei Wu's comment above, which initially fills the array with 0's, then uses the map function with a lambda to fill each element with a new array. The fill function simply fills the array with exactly what you tell it to. Does that make sense? For more info on the map function, see: developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/… Commented Sep 16, 2017 at 5:38
  • 2
    @kalehmann that is fine: meta.stackoverflow.com/a/252017/2311074 If the new question is a better question or has better answers, then vote to close the old one as a duplicate of the new one. Commented Aug 14, 2019 at 6:49

56 Answers 56

1426

Practically? Yes. You can create an array of arrays which functions as an 2D array as every item is an array itself:

let items = [
  [1, 2],
  [3, 4],
  [5, 6]
];
console.log(items[0][0]); // 1
console.log(items[0][1]); // 2
console.log(items[1][0]); // 3
console.log(items[1][1]); // 4
console.log(items);

But technically this is just an array of arrays and not a “true” 2D array, as I. J. Kennedy pointed out.

It should be noted that you could keep nesting arrays into one another and so create “multidimensional” arrays.

Sign up to request clarification or add additional context in comments.

9 Comments

It would be difficult to initialize a large multidimensional array this way. However, this function can be used to create an empty multidimensional, with the dimensions specified as parameters.
@AndersonGreen It's a good thing you mentioned a link for those interested in multi-D array solution, but the question and Ballsacian1's answer are about "2D" array, not "multi-D" array
@SashikaXP, this does not work for first indices other than 0.
The question is how to declare a two dimensional array. Which is what I was looking for and found this and following answers which fail to discern the difference between declare and initialize. There's also declaration with known length or unbounded, neither of which is discussed.
I believe this is a jagged array (array of arrays) - Does JavaScript have a difference between jagged and multidimensional as some other languages do?
|
515

You simply make each item within the array an array.

var x = new Array(10);

for (var i = 0; i < x.length; i++) {
  x[i] = new Array(3);
}

console.log(x);

7 Comments

Can they use things like strings for their keys and values? myArray['Book']['item1'] ?
@Diego, yes, but that's not what arrays are intended for. It's better to use an object when your keys are strings.
I like this example better than the accepted answer because this can be implemented for dynamically sized arrays, e.g. new Array(size) where size is a variable.
This is working, thanks. You can see the example Gargo jsfiddle.net/matasoy/oetw73sj
Doesn't work at all!! new Array?? in which language? running the snippet you get only undefined!
|
231

How to create an empty two dimensional array (one-line)

Array.from(Array(2), () => new Array(4))

2 and 4 being first and second dimensions respectively.

We are making use of Array.from, which can take an array-like param and an optional mapping for each of the elements.

Array.from(arrayLike[, mapFn[, thisArg]])

var arr = Array.from(Array(2), () => new Array(4));
arr[0][0] = 'foo';
console.info(arr);

The same trick can be used to Create a JavaScript array containing 1...N


Alternatively (but more inefficient 12% with n = 10,000)

Array(2).fill(null).map(() => Array(4))

The performance decrease comes with the fact that we have to have the first dimension values initialized to run .map. Remember that Array will not allocate the positions until you order it to through .fill or direct value assignment.

var arr = Array(2).fill(null).map(() => Array(4));
arr[0][0] = 'foo';
console.info(arr);


Follow up

Here's a method that appears correct, but has issues.

 Array(2).fill(Array(4)); // BAD! Rows are copied by reference

While it does return the apparently desired two dimensional array ([ [ <4 empty items> ], [ <4 empty items> ] ]), there a catch: first dimension arrays have been copied by reference. That means a arr[0][0] = 'foo' would actually change two rows instead of one.

var arr = Array(2).fill(Array(4));
arr[0][0] = 'foo';
console.info(arr);
console.info(arr[0][0], arr[1][0]);

9 Comments

I suggest this: Array.from({length:5}, () => [])
Subjective here but this answer (the first and second within it) seems like the best balance of succinct, fast, and modern.
Best one-liner answer!
what is the difference between Array.from(Array(2), () => new Array(4)) and Array.from(Array(2), () => Array(4))?
new Array() and Array() are the same according to MDN. both create a new Array()
There is a mistake here in that new Array(100).fill(null).map(() => new Array(100).fill(null)) is faster than Array.from({ length: 100 }, () => Array.from({ length: 100 }, () => null)); When testing arrays of all sizes (10 to 1000), Array.from is ~67% slower than new Array see: jsbench.me/z3l905yt6p/2
|
226

Similar to activa's answer, here's a function to create an n-dimensional array:

function createArray(length) {
    var arr = new Array(length || 0),
        i = length;

    if (arguments.length > 1) {
        var args = Array.prototype.slice.call(arguments, 1);
        while(i--) arr[length-1 - i] = createArray.apply(this, args);
    }

    return arr;
}

createArray();     // [] or new Array()

createArray(2);    // new Array(2)

createArray(3, 2); // [new Array(2),
                   //  new Array(2),
                   //  new Array(2)]

7 Comments

Can this create a 4 dimensional array?
@trusktr: Yes, you could create as many dimensions as you want (within your memory constraints). Just pass in the length of the four dimensions. For example, var array = createArray(2, 3, 4, 5);.
Best answer ! However, I would not recommend to use it with 0 or 1 parameters (useless)
@BritishDeveloper Yes. This is a 5D array with each length at 5: [[[[[null,null],[null,null]],[[null,null],[null,null]]],[[[null,null],[null,null]],[[null,null],[null,null]]]],[[[[null,null],[null,null]],[[null,null],[null,null]]],[[[null,null],[null,null]],[[null,null],[null,null]]]]]
@haykam sorry to waste your time - I was being sarcastic :/
|
98

Javascript only has 1-dimensional arrays, but you can build arrays of arrays, as others pointed out.

The following function can be used to construct a 2-d array of fixed dimensions:

function Create2DArray(rows) {
  var arr = [];

  for (var i=0;i<rows;i++) {
     arr[i] = [];
  }

  return arr;
}

The number of columns is not really important, because it is not required to specify the size of an array before using it.

Then you can just call:

var arr = Create2DArray(100);

arr[50][2] = 5;
arr[70][5] = 7454;
// ...

4 Comments

i want to make a 2-dim array that would represent a deck of cards. Which would be a 2-dim array that holds the card value and then in then the suit. What would be the easiest way to do that.
function Create2DArray(rows) { var arr = []; for (var i=0;i<rows;i++) { arr[i] = []; } return arr; } function print(deck) { for(t=1;t<=4;t++) { for (i=1;i<=13;i++) { document.writeln(deck[t][i]); } } } fucntion fillDeck(d) { for(t=1;t<=4;t++) { myCardDeck[t][1] = t; for (i=1;i<=13;i++) { myCardDeck[t][i] = i; } } } function loadCardDeck() { var myCardDeck = Create2DArray(13); fillDeck(myCardDeck); print(myCardDeck); }
@Doug: You actually want a one-dimensional array of objects with 2 attributes. var deck= []; deck[0]= { face:1, suit:'H'};
@DougHauf that's a minified 2D-array ?? :P :D
87

The easiest way:

var myArray = [[]];

8 Comments

which is a 2-dimension array
Yeah, careful with that. Assigning myArray[0][whatever] is fine, but try and set myArray[1][whatever] and it complains that myArray[1] is undefined.
@Philip you have to set myArray[1]=[]; before assigning myArray[1][0]=5;
Be aware, this does not "create an empty 1x1 array" as @AndersonGreen wrote. It creates a "1x0" array (i.e. 1 row containing an array with 0 columns). myArray.length == 1 and myArray[0].length == 0. Which then gives the wrong result if you then copy a "genuinely empty" "0x0" array into it.
@182764125216 that was knowledge of the day for me. Thanks :)
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46

The reason some say that it isn't possible is because a two dimensional array is really just an array of arrays. The other comments here provide perfectly valid methods of creating two dimensional arrays in JavaScript, but the purest point of view would be that you have a one dimensional array of objects, each of those objects would be a one dimensional array consisting of two elements.

So, that's the cause of the conflicting view points.

4 Comments

No, it's not. In some languages, you can have multidimensional arrays like string[3,5] = "foo";. It's a better approach for some scenarios, because the Y axis is not actually a child of the X axis.
Once it gets to the underlying machine code, all tensors of dimension > 1 are arrays of arrays, whichever language we are talking about. It is worthwhile keeping this in mind for reasons of cache optimisation. Any decent language that caters seriously for numerical computing will allow you to align your multidimensional structure in memory such that your most-used dimension is stored contiguously. Python's Numpy, Fortran, and C, come to mind. Indeed there are cases when it is worthwhile to reduce dimensionality into multiple structures for this reason.
Computers have no notion of dimensions. There is only 1 dimension, the memory address. Everything else is notational decoration for the benefit of the programmer.
@ThomasBrowne Not exactly. "Arrays of arrays" require some storage for the sizes of inner arrays (they may differ) and another pointer dereferencing to find the place where an inner array is stored. In any "decent" language multidimentional arrays differ from jagged arrays, because they're different data structures per se. (And the confusing part is that C arrays are multidimentional, even though they're indexed with [a][b] syntax.)
39

Few people show the use of push:
To bring something new, I will show you how to initialize the matrix with some value, example: 0 or an empty string "".
Reminding that if you have a 10 elements array, in javascript the last index will be 9!

function matrix( rows, cols, defaultValue){

  var arr = [];

  // Creates all lines:
  for(var i=0; i < rows; i++){

      // Creates an empty line
      arr.push([]);

      // Adds cols to the empty line:
      arr[i].push( new Array(cols));

      for(var j=0; j < cols; j++){
        // Initializes:
        arr[i][j] = defaultValue;
      }
  }

return arr;
}

usage examples:

x = matrix( 2 , 3,''); // 2 lines, 3 cols filled with empty string
y = matrix( 10, 5, 0);// 10 lines, 5 cols filled with 0

3 Comments

I remove last for (which sets default value) from your procedure and write m=matrix(3,4); m[1][2]=2; console.log(JSON.stringify(m)); - and we get very strage matrix (too much nested) - you repair it in last for-defaultValue step, but I think you can rewrite procedure to use less nested arras before setting default values.
for javascript world, this is the perfect solutions. Thank you very much for providing this solutions
You are so kind AMIC
30

Two-liner:

var a = []; 
while(a.push([]) < 10);

It will generate an array a of the length 10, filled with arrays. (Push adds an element to an array and returns the new length)

7 Comments

One-liner: for (var a=[]; a.push([])<10;);?
@Bergi will the a variable still be defined in the next line..?
@StinkyCat: Yes, that's how var works. It's always function-scoped.
I know, therefore your one-liner is useless in this case: you cannot "access its members" (check question)
domenukk and @Bergi, you're both correct. I tried it out and I can access a after the for. I apologize! and thank you, may this be a lesson to me ;)
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28

The sanest answer seems to be

var nrows = ~~(Math.random() * 10);
var ncols = ~~(Math.random() * 10);
console.log(`rows:${nrows}`);
console.log(`cols:${ncols}`);
var matrix = new Array(nrows).fill(0).map(row => new Array(ncols).fill(0));
console.log(matrix);


Note we can't directly fill with the rows since fill uses shallow copy constructor, therefore all rows would share the same memory...here is example which demonstrates how each row would be shared (taken from other answers):

// DON'T do this: each row in arr, is shared
var arr = Array(2).fill(Array(4));
arr[0][0] = 'foo'; // also modifies arr[1][0]
console.info(arr);

3 Comments

This should be at the very top. I did something similar using Array.apply(null, Array(nrows)) but this is much more elegant.
This regard my last comment... Internet Explorer and Opera don't have support for fill. This won't work on a majority of browsers.
@dimgl Fill can be emulated in this instance with a constant map: Array(nrows).map(() => 0), or, Array(nrows).map(function(){ return 0; });
24

Performance

Today 2020.02.05 I perform tests on MacOs HighSierra 10.13.6 on Chrome v79.0, Safari v13.0.4 and Firefox v72.0, for chosen solutions.

Conclusions for non-initialised 2d array

  • esoteric solution {}/arr[[i,j]] (N) is fastest for big and small arrays and it looks like it is good choice for big sparse arrays
  • solutions based on for-[]/while (A,G) are fast and they are good choice for small arrays.
  • solutions for-[] (B,C) are fast and they are good choice for big arrays
  • solutions based on Array..map/from/fill (I,J,K,L,M) are quite slow for small arrays, and quite fast for big arrays
  • surprinsingly for-Array(n) (B,C) is much slower on safari than for-[] (A)
  • surprinsingly for-[] (A) for big array is slow on all browsers
  • solutions K is slow for small arrays for all browsers
  • solutions A,E,G are slow for big arrays for all browsers
  • solution M is slowest for all arrays on all browsers

enter image description here

Conclusions for initialised 2d array

  • solutions based on for/while (A,B,C,D,E,G) are fastest/quite fast for small arrays on all browsers
  • solutions based on for (A,B,C,E) are fastest/quite fast for big arrays on all browsers
  • solutions based on Array..map/from/fill (I,J,K,L,M) are medium fast or slow for small arrays on all browsers
  • solutions F,G,H,I,J,K,L for big arrays are medium or fast on chrome and safari but slowest on firefox.
  • esoteric solution {}/arr[[i,j]] (N) is slowest for small and big arrays on all browsers

enter image description here

Details

Test for solutions which not fill (initialise) output array

We test speed of solutions for

  • small arrays (12 elements) - you can perform tests on your machine HERE
  • big arrays (1 million elements) arrays - you can perform tests on your machine HERE

function A(r) {
  var arr = [];
  for (var i = 0; i < r; i++) arr[i] = [];
  return arr;
}

function B(r, c) {
  var arr = new Array(r);
  for (var i = 0; i < arr.length; i++) arr[i] = new Array(c);
  return arr;
}

function C(r, c) {
  var arr = Array(r);
  for (var i = 0; i < arr.length; i++) arr[i] = Array(c);
  return arr;
}

function D(r, c) {
  // strange, but works
  var arr = [];
  for (var i = 0; i < r; i++) {
    arr.push([]);
    arr[i].push(Array(c));
  }
  return arr;
}

function E(r, c) {
  let array = [[]];
  for (var x = 0; x < c; x++) {
    array[x] = [];
    for (var y = 0; y < r; y++) array[x][y] = [0];
  }
  return array;
}

function F(r, c) {
  var makeArray = function(dims, arr) {
    if (dims[1] === undefined) {
      return Array(dims[0]);
    }

    arr = Array(dims[0]);

    for (var i = 0; i < dims[0]; i++) {
      arr[i] = Array(dims[1]);
      arr[i] = makeArray(dims.slice(1), arr[i]);
    }

    return arr;
  }
  return makeArray([r, c]);
}

function G(r) {
  var a = [];
  while (a.push([]) < r);
  return a;
}

function H(r,c) {
  function createArray(length) {
    var arr = new Array(length || 0),
        i = length;

    if (arguments.length > 1) {
        var args = Array.prototype.slice.call(arguments, 1);
        while(i--) arr[length-1 - i] = createArray.apply(this, args);
    }

    return arr;
  }
  return createArray(r,c);
}

function I(r, c) {
  return [...Array(r)].map(x => Array(c));
}

function J(r, c) {
  return Array(r).fill(0).map(() => Array(c));
}

function K(r, c) {
  return Array.from(Array(r), () => Array(c));
}

function L(r, c) {
  return Array.from({length: r}).map(e => Array(c));
}

function M(r, c) {
  return Array.from({length: r}, () => Array.from({length: c}, () => {}));
}

function N(r, c) {
  return {}
}



// -----------------------------------------------
// SHOW
// -----------------------------------------------

log = (t, f) => {
  let A = f(3, 4); // create array with 3 rows and 4 columns
  A[1][2] = 6 // 2-nd row 3nd column set to 6
  console.log(`${t}[1][2]: ${A[1][2]}, full: ${JSON.stringify(A).replace(/null/g,'x')}`);
}

log2 = (t, f) => {
  let A = f(3, 4); // create array with 3 rows and 4 columns
  A[[1,2]] = 6 // 2-nd row 3nd column set to 6
  console.log(`${t}[1][2]: ${A[[1,2]]}, full: ${JSON.stringify(A).replace(/null/g,'x')}`);
}

log('A', A);
log('B', B);
log('C', C);
log('D', D);
log('E', E);
log('F', F);
log('G', G);
log('H', H);
log('I', I);
log('J', J);
log('K', K);
log('L', L);
log('M', M);
log2('N', N);
This is presentation of solutions - not benchmark

Test for solutions which fill (initialise) output array

We test speed of solutions for

  • small arrays (12 elements) - you can perform tests on your machine HERE
  • big arrays (1 million elements) arrays - you can perform tests on your machine HERE

function A(r, c, def) {
  var arr = [];
  for (var i = 0; i < r; i++) arr[i] = Array(c).fill(def);
  return arr;
}

function B(r, c, def) {
  var arr = new Array(r);
  for (var i = 0; i < arr.length; i++) arr[i] = new Array(c).fill(def);
  return arr;
}

function C(r, c, def) {
  var arr = Array(r);
  for (var i = 0; i < arr.length; i++) arr[i] = Array(c).fill(def);
  return arr;
}

function D(r, c, def) {
  // strange, but works
  var arr = [];
  for (var i = 0; i < r; i++) {
    arr.push([]);
    arr[i].push(Array(c));
  }
  for (var i = 0; i < r; i++) for (var j = 0; j < c; j++) arr[i][j]=def
  return arr;
}

function E(r, c, def) {
  let array = [[]];
  for (var x = 0; x < c; x++) {
    array[x] = [];
    for (var y = 0; y < r; y++) array[x][y] = def;
  }
  return array;
}

function F(r, c, def) {
  var makeArray = function(dims, arr) {
    if (dims[1] === undefined) {
      return Array(dims[0]).fill(def);
    }

    arr = Array(dims[0]);

    for (var i = 0; i < dims[0]; i++) {
      arr[i] = Array(dims[1]);
      arr[i] = makeArray(dims.slice(1), arr[i]);
    }

    return arr;
  }
  return makeArray([r, c]);
}

function G(r, c, def) {
  var a = [];
  while (a.push(Array(c).fill(def)) < r);
  return a;
}

function H(r,c, def) {
  function createArray(length) {
    var arr = new Array(length || 0),
        i = length;

    if (arguments.length > 1) {
        var args = Array.prototype.slice.call(arguments, 1);
        while(i--) arr[length-1 - i] = createArray.apply(this, args).fill(def);
    }

    return arr;
  }
  return createArray(r,c);
}

function I(r, c, def) {
  return [...Array(r)].map(x => Array(c).fill(def));
}

function J(r, c, def) {
  return Array(r).fill(0).map(() => Array(c).fill(def));
}

function K(r, c, def) {
  return Array.from(Array(r), () => Array(c).fill(def));
}

function L(r, c, def) {
  return Array.from({length: r}).map(e => Array(c).fill(def));
}

function M(r, c, def) {
  return Array.from({length: r}, () => Array.from({length: c}, () => def));
}

function N(r, c, def) {
  let arr={};
  for (var i = 0; i < r; i++) for (var j = 0; j < c; j++) arr[[i,j]]=def;
  return arr;
}



// -----------------------------------------------
// SHOW
// -----------------------------------------------

log = (t, f) => {
  let A = f(1000,1000,7); // create array with 1000 rows and 1000 columns, 
                          // each array cell initilised by 7
  A[800][900] = 5         // 800nd row and 901nd column set to 5
  console.log(`${t}[1][2]: ${A[1][2]}, ${t}[800][901]: ${A[800][900]}`);
}

log2 = (t, f) => {
  let A = f(1000,1000,7); // create array with 1000 rows and 1000 columns, 
                          // each array cell initilised by 7
  A[[800,900]] = 5            // 800nd row 900nd column set to 5
  console.log(`${t}[1][2]: ${A[[1,2]]}, ${t}[800][900]: ${A[[800,900]]}`);
}

log('A', A);
log('B', B);
log('C', C);
log('D', D);
log('E', E);
log('F', F);
log('G', G);
log('H', H);
log('I', I);
log('J', J);
log('K', K);
log('L', L);
log('M', M);
log2('N', N);
This is presentation of solutions - not benchmark

enter image description here

Comments

23

The easiest way:

var arr  = [];

var arr1 = ['00','01'];
var arr2 = ['10','11'];
var arr3 = ['20','21'];

arr.push(arr1);
arr.push(arr2);
arr.push(arr3);

alert(arr[0][1]); // '01'
alert(arr[1][1]); // '11'
alert(arr[2][0]); // '20'

1 Comment

that's horrible, what if they array is 1000x1000? are you going to write thousands of lines?
21

To create an 4x6 array, simply do this

const x = [...new Array(6)].map(elem => new Array(4))

It's usually a good practice to start with an empty array, rather than filling w random values. (You normally declare array as const x = [] in 1D, so better to start w empty in 2D.)

Comments

19

This is what i achieved :

var appVar = [[]];
appVar[0][4] = "bineesh";
appVar[0][5] = "kumar";
console.log(appVar[0][4] + appVar[0][5]);
console.log(appVar);

This spelled me bineeshkumar

3 Comments

Notice how you can only access the 0 index of the parent array. This isn't as useful as something which allows you to set, for example, appVar[5][9] = 10; ... you would get 'Unable to set property "9" of undefined' with this.
But appVar[1][4] = "bineesh"; is wrong, how to solve it?
@RaisinBran and @Gank This creates only one row with dynamic multiple columns. If you want to have multiple rows, you can do something like this: var appVar = [[], [], [], [], [], []]; This will create 6 rows with each dynamic multiple columns.
18

Two dimensional arrays are created the same way single dimensional arrays are. And you access them like array[0][1].

var arr = [1, 2, [3, 4], 5];

alert (arr[2][1]); //alerts "4"

Comments

17

For one liner lovers Array.from()

// creates 8x8 array filed with "0"    
const arr2d = Array.from({ length: 8 }, () => Array.from({ length: 8 }, () => "0"))

Another one (from comment by dmitry_romanov) use Array().fill()

// creates 8x8 array filed with "0"    
const arr2d = Array(8).fill(0).map(() => Array(8).fill("0"))

Using ES6+ spread operator ("inspired" by InspiredJW answer :) )

// same as above just a little shorter
const arr2d = [...Array(8)].map(() => Array(8).fill("0"))

1 Comment

we can remove 0 in the first fill() function: const arr2d = Array(8).fill().map(() => Array(8).fill("0"));
15

I'm not sure if anyone has answered this but I found this worked for me pretty well -

var array = [[,],[,]]

eg:

var a = [[1,2],[3,4]]

For a 2 dimensional array, for instance.

2 Comments

How can I do this dynamically? I want the inner arrays with different sizes.
You don't need extra commas var array = [[],[]] is adequate.
15

To create a non-sparse "2D" array (x,y) with all indices addressable and values set to null:

let 2Darray = new Array(x).fill(null).map(item =>(new Array(y).fill(null))) 

bonus "3D" Array (x,y,z)

let 3Darray = new Array(x).fill(null).map(item=>(new Array(y).fill(null)).map(item=>Array(z).fill(null)))

Variations and corrections on this have been mentioned in comments and at various points in response to this question but not as an actual answer so I am adding it here.

It should be noted that (similar to most other answers) this has O(x*y) time complexity so it probably not suitable for very large arrays.

2 Comments

be careful because fill set the same value. if change null to `object it will be the same object in every column
@StanislavMayorov If you want to set each cell's value, just use the same trick: let 2Darray = new Array(x).fill(null).map(item =>(new Array(y).fill(null).map(cell =>(yourValueHere))))
13

To create a 2D array in javaScript we can create an Array first and then add Arrays as it's elements. This method will return a 2D array with the given number of rows and columns.

function Create2DArray(rows,columns) {
   var x = new Array(rows);
   for (var i = 0; i < rows; i++) {
       x[i] = new Array(columns);
   }
   return x;
}

to create an Array use this method as below.

var array = Create2DArray(10,20);

3 Comments

Please would you add some explanatory information to your ansdwer showing how it works, and why it solves the problem. This will help others who find this page in the future
When would you need an Array that is preinitialized with a certain number of colums in Javascript? You can access the n-th element of a [] array as well.
I noticed the function starts with capital C, which (by certain conventions) suggest it would be a Function constructor and you would use it with the new keyword. A very minor and somewhat opinionated maybe, but I would still suggest un-capitalized word.
12

Row and Column sizes of an array known only at the run time then following method could be used for creating a dynamic 2d array.

    var num = '123456';
    var row = 3; // Known at run time
    var col = 2; // Known at run time
    var i = 0;
    
    var array2D = [[]];
    for(var r = 0; r < row; ++r)
    {
        array2D[r] = [];
        for(var c = 0; c < col; ++c)
        {
            array2D[r][c] = num[i++];
        }
    }
    console.log(array2D); 
    // [[ '1', '2' ], 
    //  [ '3', '4' ], 
    //  [ '5', '6' ]]
    
    console.log(array2D[2][1]); // 6

1 Comment

Works well, but shouldn't col and row be swapped? Your visual representation seems to go against the convention of rows being horizontal, and columns being vertical.
11

Use Array Comprehensions

In JavaScript 1.7 and higher you can use array comprehensions to create two dimensional arrays. You can also filter and/or manipulate the entries while filling the array and don't have to use loops.

var rows = [1, 2, 3];
var cols = ["a", "b", "c", "d"];

var grid = [ for (r of rows) [ for (c of cols) r+c ] ];

/* 
         grid = [
            ["1a","1b","1c","1d"],
            ["2a","2b","2c","2d"],
            ["3a","3b","3c","3d"]
         ]
*/

You can create any n x m array you want and fill it with a default value by calling

var default = 0;  // your 2d array will be filled with this value
var n_dim = 2;
var m_dim = 7; 

var arr = [ for (n of Array(n_dim)) [ for (m of Array(m_dim) default ]] 
/* 
         arr = [
            [0, 0, 0, 0, 0, 0, 0],
            [0, 0, 0, 0, 0, 0, 0],
         ]
*/

More examples and documentation can be found here.

Please note that this is not a standard feature yet.

2 Comments

A quick google check here... yup... the for statement is still a loop...
It is not supported by any browser - HERE?
11
Array(m).fill(v).map(() => Array(n).fill(v))

You can create a 2 Dimensional array m x n with initial value m and n can be any numbers v can be any value string, number, undefined.

One approach can be var a = [m][n]

1 Comment

I like your answer, but you don't need to use map(), you can do it with fill() alone, like this: var map = new Array(height).fill(new Array(width).fill(val)); creating an array like so: map[y][x] = val;
10

The following example defines a two-dimensional array named activities:

    let activities = [
        ['Work', 9],
        ['Eat', 1],
        ['Commute', 2],
        ['Play Game', 1],
        ['Sleep', 7]
    ];

In the activities array, the first dimension represents the activity and the second one shows the number of hours spent per day for each.

To show the activities array in the console, you use the console.table() method as follows:

console.table(activities);

The following illustrates the output:

┌─────────┬─────────────┬───┐
│ (index) │      0      │ 1 │
├─────────┼─────────────┼───┤
│    0    │   'Work'    │ 9 │
│    1    │    'Eat'    │ 1 │
│    2    │  'Commute'  │ 2 │
│    3    │ 'Play Game' │ 1 │
│    4    │   'Sleep'   │ 7 │
└─────────┴─────────────┴───┘

Note that the (index) column is for the illustration that indicates the indices of the inner array.

To access an element of the multidimensional array, you first use square brackets to access an element of the outer array that returns an inner array; and then use another square bracket to access the element of the inner array.

The following example returns the second element of the first inner array in the activities array above:

console.log(activities[0][1]); // 9

Adding elements to the JavaScript multidimensional array

You can use the Array methods such as push() and splice() to manipulate elements of a multidimensional array.

For example, to add a new element at the end of the multidimensional array, you use the push() method as follows:

activities.push(['Study',2]);
┌─────────┬─────────────┬───┐
│ (index) │      0      │ 1 │
├─────────┼─────────────┼───┤
│    0    │   'Work'    │ 9 │
│    1    │    'Eat'    │ 1 │
│    2    │  'Commute'  │ 2 │
│    3    │ 'Play Game' │ 1 │
│    4    │   'Sleep'   │ 7 │
│    5    │   'Study'   │ 2 │
└─────────┴─────────────┴───┘

To insert an element in the middle of the array, you use the splice() method. The following inserts an element in the second position of the activities array:

activities.splice(1, 0, ['Programming', 2]);
┌─────────┬───────────────┬───┐
│ (index) │       0       │ 1 │
├─────────┼───────────────┼───┤
│    0    │    'Work'     │ 9 │
│    1    │ 'Programming' │ 2 │
│    2    │     'Eat'     │ 1 │
│    3    │   'Commute'   │ 2 │
│    4    │  'Play Game'  │ 1 │
│    5    │    'Sleep'    │ 7 │
│    6    │    'Study'    │ 2 │
└─────────┴───────────────┴───┘

This example calculates the percentage of the hours spent on each activity and appends the percentage to the inner array.

activities.forEach(activity => {
    let percentage = ((activity[1] / 24) * 100).toFixed();
    activity[2] = percentage + '%';
});
┌─────────┬───────────────┬───┬───────┐
│ (index) │       0       │ 1 │   2   │
├─────────┼───────────────┼───┼───────┤
│    0    │    'Work'     │ 9 │ '38%' │
│    1    │ 'Programming' │ 2 │ '8%'  │
│    2    │     'Eat'     │ 1 │ '4%'  │
│    3    │   'Commute'   │ 2 │ '8%'  │
│    4    │  'Play Game'  │ 1 │ '4%'  │
│    5    │    'Sleep'    │ 7 │ '29%' │
│    6    │    'Study'    │ 2 │ '8%'  │
└─────────┴───────────────┴───┴───────┘

Removing elements from the JavaScript multidimensional array

To remove an element from an array, you use the pop() or splice() method.

For example, the following statement removes the last element of the activities array:

activities.pop();
┌─────────┬───────────────┬───┬───────┐
│ (index) │       0       │ 1 │   2   │
├─────────┼───────────────┼───┼───────┤
│    0    │    'Work'     │ 9 │ '38%' │
│    1    │ 'Programming' │ 2 │ '8%'  │
│    2    │     'Eat'     │ 1 │ '4%'  │
│    3    │   'Commute'   │ 2 │ '8%'  │
│    4    │  'Play Game'  │ 1 │ '4%'  │
│    5    │    'Sleep'    │ 7 │ '29%' │
└─────────┴───────────────┴───┴───────┘

Similarly, you can remove the elements from the inner array of the multidimensional array by using the pop() method. The following example removes the percentage element from the inner arrays of the activities array.

activities.forEach((activity) => {
    activity.pop(2);
});
┌─────────┬───────────────┬───┐
│ (index) │       0       │ 1 │
├─────────┼───────────────┼───┤
│    0    │    'Work'     │ 9 │
│    1    │ 'Programming' │ 2 │
│    2    │     'Eat'     │ 1 │
│    3    │   'Commute'   │ 2 │
│    4    │  'Play Game'  │ 1 │
│    5    │    'Sleep'    │ 7 │
└─────────┴───────────────┴───┘

Iterating over elements of the JavaScript multidimensional array

To iterate a multidimensional array, you use a nested for loop as in the following example.

// loop the outer array

for (let i = 0; i < activities.length; i++) {
    // get the size of the inner array
    var innerArrayLength = activities[i].length;
    // loop the inner array
    for (let j = 0; j < innerArrayLength; j++) {
        console.log('[' + i + ',' + j + '] = ' + activities[i][j]);
    }
}

The first loop iterates over the elements of the outer array and the nested loop iterates over elements of the inner array.

The following shows the output of the script in the console:

[0,0] = Work
[0,1] = 9
[1,0] = Eat
[1,1] = 1
[2,0] = Commute
[2,1] = 2
[3,0] = Play Game
[3,1] = 1
[4,0] = Sleep
[4,1] = 7
[5,0] = Study
[5,1] = 2

Or you can use the forEach() method twice:

activities.forEach((activity) => {
    activity.forEach((data) => {
        console.log(data);
    });
});
Work
9
Eat
1
Commute
2
Play Game
1
Sleep
7
Study
2

1 Comment

8

My approach is very similar to @Bineesh answer but with a more general approach.

You can declare the double array as follows:

var myDoubleArray = [[]];

And the storing and accessing the contents in the following manner:

var testArray1 = [9,8]
var testArray2 = [3,5,7,9,10]
var testArray3 = {"test":123}
var index = 0;

myDoubleArray[index++] = testArray1;
myDoubleArray[index++] = testArray2;
myDoubleArray[index++] = testArray3;

console.log(myDoubleArray[0],myDoubleArray[1][3], myDoubleArray[2]['test'],) 

This will print the expected output

[ 9, 8 ] 9 123

Comments

8

I found below is the simplest way:

var array1 = [[]];   
array1[0][100] = 5; 
    
alert(array1[0][100]);
alert(array1.length);
alert(array1[0].length);

2 Comments

array1[1][100] = 666; throws Uncaught TypeError: Cannot set property '100' of undefined
@KamilKiełczewski you are right, looks like this only initiate for the first array of array, for the second before you do array1[1][100] = 666;, you need to do this array1[1] = [];.
7

var playList = [
  ['I Did It My Way', 'Frank Sinatra'],
  ['Respect', 'Aretha Franklin'],
  ['Imagine', 'John Lennon'],
  ['Born to Run', 'Bruce Springsteen'],
  ['Louie Louie', 'The Kingsmen'],
  ['Maybellene', 'Chuck Berry']
];

function print(message) {
  document.write(message);
}

function printSongs( songs ) {
  var listHTML;
  listHTML = '<ol>';
  for ( var i = 0; i < songs.length; i += 1) {
    listHTML += '<li>' + songs[i][0] + ' by ' + songs[i][1] + '</li>';
  }
  listHTML += '</ol>';
  print(listHTML);
}

printSongs(playList);

Comments

6

Below one, creates a 5x5 matrix and fill them with null

var md = [];
for(var i=0; i<5; i++) {
    md.push(new Array(5).fill(null));
}

console.log(md);

1 Comment

This answer is wrong. It will create an array with same array filling in its slots. md[1][0] = 3 and all the rest of elements are updated too
6

ES6+, ES2015+ can do this in even simpler way


Creating 3 x 2 Array filled with true

[...Array(3)].map(item => Array(2).fill(true))

1 Comment

I need to confess. I "adopted" your answer and added to mine, the one-liners collection.
5

I had to make a flexible array function to add "records" to it as i needed and to be able to update them and do whatever calculations e needed before i sent it to a database for further processing. Here's the code, hope it helps :).

function Add2List(clmn1, clmn2, clmn3) {
    aColumns.push(clmn1,clmn2,clmn3); // Creates array with "record"
    aLine.splice(aPos, 0,aColumns);  // Inserts new "record" at position aPos in main array
    aColumns = [];    // Resets temporary array
    aPos++ // Increments position not to overlap previous "records"
}

Feel free to optimize and / or point out any bugs :)

1 Comment

How about just aLine.push([clmn1, clmn2, clmn3]); ?
5

Javascript does not support two dimensional arrays, instead we store an array inside another array and fetch the data from that array depending on what position of that array you want to access. Remember array numeration starts at ZERO.

Code Example:

/* Two dimensional array that's 5 x 5 

       C0 C1 C2 C3 C4 
    R0[1][1][1][1][1] 
    R1[1][1][1][1][1] 
    R2[1][1][1][1][1] 
    R3[1][1][1][1][1] 
    R4[1][1][1][1][1] 
*/

var row0 = [1,1,1,1,1],
    row1 = [1,1,1,1,1],
    row2 = [1,1,1,1,1],
    row3 = [1,1,1,1,1],
    row4 = [1,1,1,1,1];

var table = [row0,row1,row2,row3,row4];
console.log(table[0][0]); // Get the first item in the array

Comments

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