Develop Reference

How to compress an array to reduce its number of elements in Javascript?

I have an array containing numbers, in that array there're some numbers that occur many times in consecutive order one after the other, and I want to compress those repeated numbers into a very specific format 'Number*Times' to reduce the size of the array:
input: [0, 1, 2, 0, 0, 0, 3, 2, 0, 0, 0, 0, 0, 0, 5, 6, 0]
---------^^^^^^^^^-----^^^^^^^^^^^^^^^^^^^--------
output: [0, 1, 2,'0x3', 3, 2, '0x6', 5, 6, 0]
let array = [0, 1, 2, 0, 0, 0, 3, 2, 0, 0, 0, 0, 0, 0, 5, 6, 0];
let string = array.toString();
let string_compressed = string.replace(/(\d+,)(\1)+/g, (x) => {
return "Number*" + x.split(",").length + ",";
});
let array_compressed = string_compressed
.split(",")
.map((x) => (isNaN(Number(x)) ? x : Number(x)));
console.log(array_compressed); //[0, 1, 2, 'Number*4', 3, 2, 'Number*7', 5, 6, 0]
I don't know how to get the number that repeated so I put Number instead!
I used regex to solve it, I know if you think to solve problem with regex, they become two problems!
BUT Guys I'm sure this isn't the efficient way to solve this problem, And there're other ways to solve it!
what do you suggest if you want to solve this problem?

Because your regex to find how many numbers repeat already only matches numbers that are in consecutive order in your array, you can simply just take the first index of the x.split(",") array and return that.
Edit:
Also, as #qrsngky out, your x.split(",").length wasn't actually the right length, because when you split it by comma, there is a null character at the end:
let array = [0, 1, 2, 0, 0, 0, 3, 2, 0, 0, 0, 0, 0, 0, 5, 6, 0];
let string = array.toString();
let string_compressed = string.replace(/(\d+,)(\1)+/g, (x) => {
console.log(x.split(","));
return "Number*" + x.split(",").length + ",";
});
let array_compressed = string_compressed
.split(",")
.map((x) => (isNaN(Number(x)) ? x : Number(x)));
console.log(array_compressed);
Sorry for missing that, and props to the comments! I just fixed it by subtracting one from the length.
Edit 2:
For edge cases, we can just add a comma and use slice.
I attached the complete fixed code snippet below:
let array = [0, 1, 2, 0, 0, 0, 3, 2, 0, 0, 0, 0, 0, 0, 5, 6, 0, 0, 0];
let string = array.toString() + ",";
let string_compressed = string.replace(/(\d+,)(\1)+/g, (x) => {
return x.split(",")[0] + "*" + (x.split(",").length - 1) + ",";
});
let array_compressed = string_compressed
.slice(0, -1)
.split(",")
.map((x) => (isNaN(Number(x)) ? x : Number(x)));
console.log(array_compressed);

Assume your original array consists of none other than numbers.
Non-regex approach: based on a for loop and counting how many repetitions had been encountered.
let array = [0, 1, 2, 0, 0, 0, 3, 2, 0, 0, 0, 0, 0, 0, 5, 6, 0]
let buffer = [];
let currentNum = array[0], count = 1;
for (let i = 1; i < array.length; i++) {
if (array[i] === currentNum) {
++count;
} else {
buffer.push( count === 1 ? currentNum : (currentNum + 'x' + count) );
currentNum = array[i];
count = 1;
}
}
//don't forget the last number
if(currentNum !== undefined) buffer.push( count === 1 ? currentNum : (currentNum + 'x' + count) );
console.log(buffer);
The if(currentNum !== undefined) check is only useful in case it's an empty array.

Another example of how not to do it with string manipulation by coding what you want done:
function packArray(array) {
var packed = [];
for( var i = 0; i < array.length; i=j) {
var entry = array[i];
for(var j = i+1; array[j] === entry && j<array.length; ++j);
packed.push( j > i+1 ? `${entry}x${j-i}` : entry);
}
return packed;
}
console.log( packArray([0, 1, 2, 0, 0, 0, 3, 2, 0, 0, 0, 0, 0, 0, 5, 6, 0]))
You could substitute let for var except for var j which should remain the same to allow access to j outside the nested for loop.

How to replace all pixels of a certain RGB value with another value in opencv4nodejs

I used opencv4nodejs and nodejs for that,
I am trying to get image RGB value and replace specific RGB values in a specific index and create a 2d array.
const color_map = [[255,255,0], [255,0,0], [0,255,255], [0,255,0], [0,0,0]];
const input_image = cv.imread("Data/IMG/train_labels/0.png");
let index = 0
function form_2D_label(mat) {
const image = mat.cvtColor(cv.COLOR_BGR2RGB);
const imageBuffer = mat.getData();
const ui8 = new Uint8Array(imageBuffer);
const imageData = new Array((image.rows * image.cols))
for (let i = 0; i < ui8.length; i += 3) {
imageData[index] = [ui8[i], ui8[i + 1], ui8[i + 2]];
for (const [index, element] of color_map.entries()) { // enumerate color map
// console.log(index, element);
// I am trying todo if imageData[index] value = [255, 255, 0] as 0, if [255, 0, 0] as 1, if [0, 255, 255] as 2 like this..
}
console.log(imageData[index]) // [255, 255, 0] / [255, 0, 0] like this
index++;
}
return imageData;
}
const test = form_2D_label(input_image);
console.log(test);
current output
[
[ 0, 0, 0 ], [ 255, 0, 0 ], [ 0, 0, 0 ], [ 255, 0, 0 ], [ 0, 0, 0 ],[255, 255, 0]
]
expected one
[
[ 4, 1, 4, 1, 4, 0 ]
]

You have a few problems with your question.
First of all color_map only has 5 elements, yet the expected result has index from 0 to 5 (6 elements), I assume that was a mistake and you just want the real indexes.
Second of all nowhere in your code is the value index assigned so I'm just gonna assume, it's the next available index, and use push property instead.
Since you don't actually want to return multidimentional array but just the 2d array of indexes, there is no point in returning the imageData.
Granted the condition you explained in the comments section that color map values will be the only things present you could try to do:
const color_map = [[255,255,0], [255,0,0], [0,255,255], [0,255,0], [0,0,0]];
function form_2D_label(mat) {
const image = mat.cvtColor(cv.COLOR_BGR2RGB);
const imageBuffer = mat.getData();
const ui8 = new Uint8Array(imageBuffer);
const imageData = [];
for (let i = 0; i < ui8.length; i += 3) {
imageData.push([ui8[i], ui8[i + 1], ui8[i + 2]]);
console.log(imageData[imageData.length - 1])
}
return [imageData.map(el => color_map.findIndex(color => arrayEquals(color, el)))];
}
function arrayEquals(array1, array2) {
for (let i = 0, l = array2.length; i < l; i++) {
if (array2[i] !== array1[i]) return false;
}
return true;
}

How/Best way to create a 2d array to store integers, JQuery/javascript

I'm trying to make a small game similar to minesweeper or battleship and I need to use some kind of 10x10 grid. To store information for this grid I was planning to use a 10x10 2d array. My problem so far is that I can't figure out how to access, check, and change the contents of the individual locations of the array. My questions is this. How, or what is the best way to create an array or something else to store the series of integers I need and later access them as necessary?
I've tried some different ways to do this, with my last attempt being:
var row1 = [0, 0, 0, 0, 0, 0, 0, 0, 0, 0];
var row2 = [0, 0, 0, 0, 0, 0, 0, 0, 0, 0];
var row3 = [0, 0, 0, 0, 0, 0, 0, 0, 0, 0];
var row4 = [0, 0, 0, 0, 0, 0, 0, 0, 0, 0];
var row5 = [0, 0, 0, 0, 0, 0, 0, 0, 0, 0];
var row6 = [0, 0, 0, 0, 0, 0, 0, 0, 0, 0];
var row7 = [0, 0, 0, 0, 0, 0, 0, 0, 0, 0];
var row8 = [0, 0, 0, 0, 0, 0, 0, 0, 0, 0];
var row9 = [0, 0, 0, 0, 0, 0, 0, 0, 0, 0];
var row10= [0, 0, 0, 0, 0, 0, 0, 0, 0, 0];
var coords = [row1, row2, row3, row4, row5, row6, row7, row8, row9, row10];
I intended to have 0 signify an unclicked space, 1 signify a clicked space that didn't contain anything, and 2 signify a space that contained an object.

Here's a way to initialize a 10x10 2D array with the number 0.
Create a single array and push 10 arrays into it. For each of those inner-arrays, push the number 0 (or whatever value you like).
var grid = [];
for (var i = 0; i < 10; i++) {
grid.push([]);
for (var j = 0; j < 10; j++) {
grid[i].push(0);
}
}
document.write(grid.join("<br>"));

I intended to have 0 signify an unclicked space, 1 signify a clicked space that didn't contain anything, and 2 signify a space that contained an object.
You need two MD arrays: one for storing values 0 1 or 2, and one for storing your objects - null or otherwise.
My problem so far is that I can't figure out how to access, check, and change the contents of the individual locations of the array.
Below is an example that uses two arrays: one to store the state of the user clicks, and another to store the related objects. When a user clicks zero to update its state, it's up to you to do something with the objs array. All I've done is change the clicked element's innerHTML to 2 when the associated object exists in the objs array, or 1 when it doesn't.
//all elements are unclicked
var ints = [
[0,0,0,0],
[0,0,0,0],
[0,0,0,0],
[0,0,0,0]
];
//objects exist where not null
var objs = [
[7,null,null,1],
[null,7,null,null],
[1,null,8,8],
[2,null,2,null]
];
//the game is the parent container
var game = $('#game');
//fill the game with rows and columns of clickable html
for(var i = 0; i < objs.length; i++) {
$(game).append('<div class="row">');
for(var j = 0; j < objs[i].length; j++) {
//store i and j indices in data attributes - used in click event
$(game).append('<div data-i="' + i + '" data-j="' + j + '" class="column">' + ints[i][j] + '</div>');
}
$(game).append('</div>');
}
//onclick - look for object in objs array (they are not null when present)
$('.column').click(function() {
var i = $(this).data('i');
var j = $(this).data('j')
//update inner html
if(objs[i][j] !== null) {
$(this).html('2');
} else {
$(this).html('1');
}
});
.column {
display: inline-block;
width: 20px;
padding: 5px;
margin: 3px;
cursor: pointer;
cursor: hand;
}
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script>
<div id="game"></div>

Try this. It will create two dimensional array with 3 rows and 3 columns. It will also assign all elements with 0 as I used fill(). And you can access any element using row and column index. In the following example I have printed first row.
var arr = new Array(3).fill(new Array(3).fill(0));
document.write(JSON.stringify(arr[0]));

You can use new Array() to create an array.
var coords = new Array(10);
for (var row = 0; row < 10; row++) {
coords[row] = new Array(10);
for (var col = 0; col < 10; col++) {
coords[row][col] = 0;
}
}

Convert JSON data into format in Highcharts' basic line chart

Using Javascript, I am trying to convert some JSON data into the format used in Highcharts' basic line chart.
What I have to start with:
originalArray = [
['valueA', 1],
['valueA', 0],
['valueB', 9],
['valueB', 9],
['valueB', 3],
['valueC', 11]
]
And what I'm trying to create using the above:
desiredArray = [{
name: 'valueA',
data: [1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]
}, {
name: 'valueB',
data: [0, 0, 0, 1, 0, 0, 0, 0, 0, 2, 0, 0]
}, {
name: 'valueC',
data: [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1]
}]
For some additional context, the 0-11 in originalArray[i][1] references a month (0 = January), and the desiredArray is a list of unique names and a count of their occurrences by month.
So far, I can:
Convert the data into a new array of objects
For each unique name in originalArray
Create a new object in the desiredArray, and set the name attribute
Add a data attribute that contains an empty array
But then I run into trouble, and can't figure out how to:
Loop through the originalArray
If the name in the originalArray matches the name in the desiredArray
Increment a counter in the matching seriesArray[i].data array, using the value of originalArray[i][1] as the index (it always be 0-11).
So I'm asking:
What's a good way to iterate across my originalArray, match up unique values, and then act only on those matches to push to the desiredArray.
What's the best way to increment the counters in desiredArray[i].data
I'm open to using libraries, such as underscore.js. Have been trying to figure this out for a couple of days now, so pretty much anything goes within the bounds of Javascript.

Updated with proper array initialization, now.
var max = originalArray.reduce(function(p,c){return Math.max(p,c[1]);},0);
var initSums = function(size) {
var arr = new Array(size);
for (var i=0;i<size;i++)
arr[i]=0;
return arr;
}
var map = originalArray.reduce(function(sums,val){
if (!sums.hasOwnProperty(val[0])) {
sums[val[0]] = initSums(max+1);
}
sums[val[0]][val[1]]++;
return sums;
},{});
var desiredArray = Object.keys(map).map(function(key) {
return {name: key, data: map[key]};
});
What we're doing here is a multi-step process:
Decide how big our arrays are going to need to be, by first scanning for the largest value in the original array.
Use an object to aggregate the counts (using Array.reduce()).
Transform the object and its properties into an array of name/data pair objects (using Array.map).

Edit: An improvement on S McCochran's solution, skipping the extraneous search for the maximum value in originalArray, since there should always be 12 elements of each data array, one per month.
function formatForHighcharts(array) {
// Create a map from value name to array of month counts
var map = originalArray.reduce(function(sums, pair) {
var key = pair[0], val = pair[1];
if(!(key in sums))
sums[key] = [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0];
// val is the month index, which corresponds directly to array index, so increase that
sums[key][val]++;
return sums;
}, {});
// Map the object to an array of { name: ..., data: ... } pairs
var formatted = Object.keys(map).map(function (key) {
return { name: key, data: map[key] };
});
return formatted;
}
Usage:
var desiredArray = formatForHighcharts(originalArray);

Declare an empty two-dimensional array in Javascript?

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 will be dynamically generated by user input.
Example of pre-defined 2d array:
var Arr=[[1,2],[3,4],[5,6]];
I guess I can use the PUSH method to add a new record at the end of the array.
How do I declare an empty two dimensional array so that when I use my first Arr.push() it will be added to the index 0, and every next record written by push will take the next index?
This is probably very easy to do, I'm just a newbie with JS, and I would appreciate if someone could write a short working code snippet that I could examine. Thanks

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 ]

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.

ES6
Matrix m with size 3 rows and 5 columns (remove .fill(0) to not init by zero)
[...Array(3)].map(_=>Array(5).fill(0))
let Array2D = (r,c) => [...Array(r)].map(_=>Array(c).fill(0));
let m = Array2D(3,5);
m[1][0] = 2; // second row, first column
m[2][4] = 8; // last row, last column
// print formated array
console.log(JSON.stringify(m)
.replace(/(\[\[)(.*)(\]\])/g,'[\n [$2]\n]').replace(/],/g,'],\n ')
);

If you want to be able access the matrix like so:
matrix[i][j]
I find it the most convenient to init it in a loop.
var matrix = [],
cols = 3;
//init the grid matrix
for ( var i = 0; i < cols; i++ ) {
matrix[i] = [];
}
This will give you
[ [], [], [] ]
so
matrix[0][0]
matrix[1][0]
returns undefined and not the error "Uncaught TypeError: Cannot set property '0' of undefined".

You can nest one array within another using the shorthand syntax:
var twoDee = [[]];

You can try something like this:-
var arr = new Array([]);
Push data:
arr[0][0] = 'abc xyz';

An empty array is defined by omitting values, like so:
v=[[],[]]
a=[]
b=[1,2]
a.push(b)
b==a[0]

You can fill an array with arrays using a function:
var arr = [];
var rows = 11;
var columns = 12;
fill2DimensionsArray(arr, rows, columns);
function fill2DimensionsArray(arr, rows, columns){
for (var i = 0; i < rows; i++) {
arr.push([0])
for (var j = 0; j < columns; j++) {
arr[i][j] = 0;
}
}
}
The result is:
Array(11)
0:(12) [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]
1:(12) [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]
2:(12) [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]
3:(12) [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]
4:(12) [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]
5:(12) [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]
6:(12) [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]
7:(12) [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]
8:(12) [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]
9:(12) [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]
10:(12)[0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]

One Liner
let m = 3 // rows
let n = 3 // columns
let array2D = Array(m).fill().map(entry => Array(n))
This implementation creates a unique subarray for each entry. So setting array2D[0][1] = 'm' does not set each entry's [1] index to 'm'

I know this is an old thread but I'd like to suggest using an array of objects rather than an array of arrays. I think it make the code simpler to understand and update.
// Use meaningful variable names like 'points',
// anything better than a bad pirate joke, 'arr'!
var points = [];
// Create an object literal, then add it to the array
var point = {x: 0, y: 0};
points.push(point);
// Create and add the object to the array in 1 line
points.push({x:5, y:5});
// Create the object from local variables
var x = 10;
var y = 8;
points.push({x, y});
// Ask the user for a point too
var response = prompt("Please enter a coordinate point. Example: 3,8");
var coords = response.split(",").map(Number);
points.push({x: coords[0], y: coords[1]});
// Show the results
var canvas = document.getElementById('graph');
var painter = canvas.getContext("2d");
var width = canvas.width, height = canvas.height;
var scale = 10, radius = 3.5, deg0 = 0, deg360 = 2 * Math.PI;
painter.beginPath();
for (var point of points) {
var x = point.x * scale + scale;
var y = height - point.y * scale - scale;
painter.moveTo(x + radius, y);
painter.arc(x, y, radius, deg0, deg360);
painter.fillText(`${point.x}, ${point.y}`, x + radius + 1, y + radius + 1);
}
painter.stroke();
<canvas id="graph" width="150" height="150" style="border: 1px solid red;"></canvas>

This one should work:
const arr = new Array(5).fill().map(_ => new Array(5).fill(0)) // ✅
You may ask why did I use map instead of:
const badArr = new Array(5).fill(new Array(5).fill(0)) // ❌
The problem with the example above is that it adds references to the array that was passed into the fill method:
While this one works fine:

const grid = Array.from(Array(3), e => Array(4));
Array.from(arrayLike, mapfn)
mapfn is called, being passed the value undefined, returning new Array(4).
An iterator is created and the next value is repeatedly called. The value returned from next, next().value is undefined. This value, undefined, is then passed to the newly-created array's iterator. Each iteration's value is undefined, which you can see if you log it.
var grid2 = Array.from(Array(3), e => {
console.log(e); // undefined
return Array(4); // a new Array.
});

ES6
const rows = 2;
const columns = 3;
const matrix = [...Array(rows)].map(() => [...Array(columns)].fill(0));
console.log(matrix);

Create an object and push that object into an array
var jSONdataHolder = function(country, lat, lon) {
this.country = country;
this.lat = lat;
this.lon = lon;
}
var jSONholderArr = [];
jSONholderArr.push(new jSONdataHolder("Sweden", "60", "17"));
jSONholderArr.push(new jSONdataHolder("Portugal", "38", "9"));
jSONholderArr.push(new jSONdataHolder("Brazil", "23", "-46"));
var nObj = jSONholderArr.length;
for (var i = 0; i < nObj; i++) {
console.log(jSONholderArr[i].country + "; " + jSONholderArr[i].lat + "; " +
jSONholderArr[i].lon);
}

var arr = [];
var rows = 3;
var columns = 2;
for (var i = 0; i < rows; i++) {
arr.push([]); // creates arrays in arr
}
console.log('elements of arr are arrays:');
console.log(arr);
for (var i = 0; i < rows; i++) {
for (var j = 0; j < columns; j++) {
arr[i][j] = null; // empty 2D array: it doesn't make much sense to do this
}
}
console.log();
console.log('empty 2D array:');
console.log(arr);
for (var i = 0; i < rows; i++) {
for (var j = 0; j < columns; j++) {
arr[i][j] = columns * i + j + 1;
}
}
console.log();
console.log('2D array filled with values:');
console.log(arr);

The most simple way to create an empty matrix is just define it as an empty array:
// Empty data structure
const matrix = []
However, we want to represent something similar to a grid with n and m parameters know ahead then we can use this instead.
// n x m data structure
const createGrid = (n, m) => [...Array(n)].map(() => [...Array(m)].fill(0))
const grid = createGrid(3, 5)
Here is a simple snippet showing how to use them.
const createGrid = (n, m) => [...Array(n)].map(() => [...Array(m)].fill(0))
const toString = m => JSON.stringify(m)
.replace(/(\[\[)(.*)(]])/g, '[\n [$2]\n]')
.replace(/],/g, '],\n ')
// Empty data structure
const matrix = []
console.log(toString(matrix))
matrix.push([1,2,3])
matrix.push([4,5,6])
matrix.push([7,8,9])
console.log(toString(matrix))
// n x m data structure
const grid = createGrid(3, 5)
console.log(toString(grid))

No need to do so much of trouble! Its simple
This will create 2 * 3 matrix of string.
var array=[];
var x = 2, y = 3;
var s = 'abcdefg';
for(var i = 0; i<x; i++){
array[i]=new Array();
for(var j = 0; j<y; j++){
array[i].push(s.charAt(counter++));
}
}

If we don’t use ES2015 and don’t have fill(), just use .apply()
See https://stackoverflow.com/a/47041157/1851492
let Array2D = (r, c, fill) => Array.apply(null, new Array(r))
.map(function() {
return Array.apply(null, new Array(c))
.map(function() {return fill})
})
console.log(JSON.stringify(Array2D(3,4,0)));
console.log(JSON.stringify(Array2D(4,5,1)));

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 );} );

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"

const dp=new Array(3).fill(new Array(3).fill(-1))
It will create below array:
[ [ -1, -1, -1 ], [ -1, -1, -1 ], [ -1, -1, -1 ] ]

You can nest a new array as you fill the first one:
let ROWS = 2,
COLS = 6;
let arr = new Array(ROWS).fill(new Array(COLS).fill(-1));
Output:
arr =
[
[-1, -1, -1, -1, -1, -1],
[-1, -1, -1, -1, -1, -1]
]
If you're confused, lets break this down with declaring/filling 1 array:
Make a new array size d, filled with any initial value
let arr1d = new Array(d).fill(<whatever_fill_val>);
Now, instead of filling your first array with a int/string/etc, you can fill it with ANOTHER array, as you fill the nested one!
let arr = new Array(d).fill(new Array(n).fill(-1));

// for 3 x 5 array
new Array(3).fill(new Array(5).fill(0))