Develop Reference

Get 3x3 blocks from 9x9 2d array as String

I am learning Javascript and currently found myself with the following problem. I need to get each individual 3x3 block of a 9x9 2d array as a string, separated by commas.
What I mean is, for example, let's say I have the following array:
var 2dArray = [
[5, 3, 5, 6, 7, 8, 9, 1, 2],
[6, 7, 1, 1, 9, 5, 3, 4, 8],
[1, 9, 2, 3, 4, 2, 5, 6, 7],
[8, 5, 9, 7, 6, 1, 4, 2, 3],
[4, 2, 6, 5, 5, 3, 7, 9, 1],
[7, 1, 3, 1, 2, 4, 8, 5, 6],
[9, 6, 1, 5, 3, 7, 2, 8, 4],
[2, 8, 7, 5, 1, 9, 6, 3, 5],
[3, 4, 5, 6, 8, 6, 1, 7, 9] ]
The result should be something like 535671192,678195342, 912348657, ... and so on, until the string is made of all the 3x3 blocks.
I thought that making nested for loops would be the best approach, but got confused along the way and I would appreciate your help.
Thank you.

You can use two loops to iterate over the positions of all the possible top left corners and another two loops to get all the elements in that square.
var arr = [
[5, 3, 5, 6, 7, 8, 9, 1, 2],
[6, 7, 1, 1, 9, 5, 3, 4, 8],
[1, 9, 2, 3, 4, 2, 5, 6, 7],
[8, 5, 9, 7, 6, 1, 4, 2, 3],
[4, 2, 6, 5, 5, 3, 7, 9, 1],
[7, 1, 3, 1, 2, 4, 8, 5, 6],
[9, 6, 1, 5, 3, 7, 2, 8, 4],
[2, 8, 7, 5, 1, 9, 6, 3, 5],
[3, 4, 5, 6, 8, 6, 1, 7, 9]
];
let res = [];
for (let i = 0; i < 9; i += 3) {
for (let j = 0; j < 9; j += 3) {
let curr = "";
for (let k = 0; k < 3; k++) {
for (let l = 0; l < 3; l++) {
curr += arr[i + k][j + l];
}
}
res.push(curr);
}
}
console.log(res);

The issue can also be solved by loops but it's good practice to solve it using the Array.map() function.
let arrayRow = "";
const resultArray = Array2d.map((element, index) => {
return arrayRow + element.map((element, i) => {
return element.toString();
});
});

you should try like this too.
var arr = [
[5, 3, 5, 6, 7, 8, 9, 1, 2],
[6, 7, 1, 1, 9, 5, 3, 4, 8],
[1, 9, 2, 3, 4, 2, 5, 6, 7],
[8, 5, 9, 7, 6, 1, 4, 2, 3],
[4, 2, 6, 5, 5, 3, 7, 9, 1],
[7, 1, 3, 1, 2, 4, 8, 5, 6],
[9, 6, 1, 5, 3, 7, 2, 8, 4],
[2, 8, 7, 5, 1, 9, 6, 3, 5],
[3, 4, 5, 6, 8, 6, 1, 7, 9]
];
let res = [];
let i = 0,j = 0;
let justOneStr = "";
while(i < 9 && j < 9){
justOneStr += arr[i][j];
if(i % 3 == 2 && j % 3 == 2){
res.push(justOneStr);
justOneStr="";
}
if((j % 9 == 8 || j % 3 == 2) && i % 3 != 2){
j -= 3;
i += 1;
}
else if(j % 9 == 8 && i % 3 == 2){
j -= 9;
i += 1;
}
else if(i % 3 == 2 && j % 3 == 2){
i -= 2;
}
j++;
}
console.log(res);

Here's a fairly straightforward nested reduce() that returns an array of matrices of the specified size. It touches each element once, and uses the coordinates in the passed matrix to determine which sub-matrix and sub-matrix row to accumulate into.
const
matrix = [
[5, 3, 5, 6, 7, 8, 9, 1, 2],
[6, 7, 1, 1, 9, 5, 3, 4, 8],
[1, 9, 2, 3, 4, 2, 5, 6, 7],
[8, 5, 9, 7, 6, 1, 4, 2, 3],
[4, 2, 6, 5, 5, 3, 7, 9, 1],
[7, 1, 3, 1, 2, 4, 8, 5, 6],
[9, 6, 1, 5, 3, 7, 2, 8, 4],
[2, 8, 7, 5, 1, 9, 6, 3, 5],
[3, 4, 5, 6, 8, 6, 1, 7, 9]],
subdivide = (matrix, width, height) => {
return matrix.reduce((acc, row, i) => {
row.reduce((_acc, x, j, row) => {
const grid = Math.floor(j / width) + Math.floor(i / height) * (Math.ceil(row.length / width));
const gridRow = i % height;
_acc[grid] ??= [];
(_acc[grid][gridRow] ??= []).push(x);
return _acc;
}, acc)
return acc;
}, [])
},
subdividedmatrix = subdivide(matrix, 3, 3);
// log submatrices
subdividedmatrix.forEach(m => console.log(JSON.stringify(m)));
// map to strings
console.log(subdividedmatrix.map(submatrix => submatrix.flat().join('')))
.as-console-wrapper { max-height: 100% !important; top: 0; }

Passing an array to a function parameter and getting values from nested array

I got stuck while practicing credit card checker practice.
My code:
// All valid credit card numbers
const valid1 = [4, 5, 3, 9, 6, 7, 7, 9, 0, 8, 0, 1, 6, 8, 0, 8]
const valid2 = [5, 5, 3, 5, 7, 6, 6, 7, 6, 8, 7, 5, 1, 4, 3, 9]
const valid3 = [3, 7, 1, 6, 1, 2, 0, 1, 9, 9, 8, 5, 2, 3, 6]
const valid4 = [6, 0, 1, 1, 1, 4, 4, 3, 4, 0, 6, 8, 2, 9, 0, 5]
const valid5 = [4, 5, 3, 9, 4, 0, 4, 9, 6, 7, 8, 6, 9, 6, 6, 6]
// All invalid credit card numbers
const invalid1 = [4, 5, 3, 2, 7, 7, 8, 7, 7, 1, 0, 9, 1, 7, 9, 5]
const invalid2 = [5, 7, 9, 5, 5, 9, 3, 3, 9, 2, 1, 3, 4, 6, 4, 3]
const invalid3 = [3, 7, 5, 7, 9, 6, 0, 8, 4, 4, 5, 9, 9, 1, 4]
const invalid4 = [6, 0, 1, 1, 1, 2, 7, 9, 6, 1, 7, 7, 7, 9, 3, 5]
const invalid5 = [5, 3, 8, 2, 0, 1, 9, 7, 7, 2, 8, 8, 3, 8, 5, 4]
// Can be either valid or invalid
const mystery1 = [3, 4, 4, 8, 0, 1, 9, 6, 8, 3, 0, 5, 4, 1, 4]
const mystery2 = [5, 4, 6, 6, 1, 0, 0, 8, 6, 1, 6, 2, 0, 2, 3, 9]
const mystery3 = [6, 0, 1, 1, 3, 7, 7, 0, 2, 0, 9, 6, 2, 6, 5, 6, 2, 0, 3]
const mystery4 = [4, 9, 2, 9, 8, 7, 7, 1, 6, 9, 2, 1, 7, 0, 9, 3]
const mystery5 = [4, 9, 1, 3, 5, 4, 0, 4, 6, 3, 0, 7, 2, 5, 2, 3]
// An array of all the arrays above
const batch = [valid1, valid2, valid3, valid4, valid5, invalid1, invalid2, invalid3, invalid4, invalid5, mystery1, mystery2, mystery3, mystery4, mystery5]
// Add your functions below:
const validateCred = (array)=> {
let tempArrSub = []; //Holds values of the 9 subtracted from doubled elements bigger than 9
let tempArr = array; //Copies the values of the array passed into parameters
tempArr.pop();
tempArr.reverse();
for (let i = tempArr.length-1; i >=0; i-=2){ //Doubles every two elements from right to left
tempArr[i] *= 2;
}
for (let k = 0; k < tempArr.length; k++) { //Subtract 9 from every second element (right to left) if bigger than 9
if (tempArr[k] > 9){
tempArrSub.push(tempArr[k] - 9);
}
else {
tempArrSub.push(tempArr[k]);
}
}
let tempArrSum = 0;
for (let m = 0; m < tempArrSub.length; m++){ //Calculates the sum of all elements in the array
tempArrSum += tempArrSub[m];
}
tempArrSum += array.pop(); //Adds the last digit of initial array to the sum
if (tempArrSum % 10 === 0) { //Returns true if the sum is divisible by 10
return true;
}
else {
return false;
}
} //End Of Function
const findInvalidCards = (nestedArray) => {
let invalidCards = [];
let validCards = [];
for (let a = 0; a < nestedArray.length; a++){
if ( validateCred(nestedArray[a]) == true ) {
validCards.push(nestedArray[a]);
}
else {
invalidCards.push(nestedArray[a]);
}
}
console.log("Invalid cards: \n" + invalidCards);
console.log("Valid cards: \n" + validCards);
}
I checked all arrays one by one passing as an argument to validateCred() function. It's working and returning true or false for each credit card.
In order to automate process I wanted findInvalidCards() to find valid or invalid cards by calling validateCred() function inside itself and returning boolean value for each card.
Here I got stuck. Because it is returning true for the 1st card and false for the remaining cards. I've been playing with the code for the whole day, but I could not move forward. I rely on your help. Thanks in advance

I don't know if is it helpful to you or not. But I rewrite your code with an optimal way.
// All valid credit card numbers
const valid1 = [4, 5, 3, 9, 6, 7, 7, 9, 0, 8, 0, 1, 6, 8, 0, 8]
const valid2 = [5, 5, 3, 5, 7, 6, 6, 7, 6, 8, 7, 5, 1, 4, 3, 9]
const valid3 = [3, 7, 1, 6, 1, 2, 0, 1, 9, 9, 8, 5, 2, 3, 6]
const valid4 = [6, 0, 1, 1, 1, 4, 4, 3, 4, 0, 6, 8, 2, 9, 0, 5]
const valid5 = [4, 5, 3, 9, 4, 0, 4, 9, 6, 7, 8, 6, 9, 6, 6, 6]
// All invalid credit card numbers
const invalid1 = [4, 5, 3, 2, 7, 7, 8, 7, 7, 1, 0, 9, 1, 7, 9, 5]
const invalid2 = [5, 7, 9, 5, 5, 9, 3, 3, 9, 2, 1, 3, 4, 6, 4, 3]
const invalid3 = [3, 7, 5, 7, 9, 6, 0, 8, 4, 4, 5, 9, 9, 1, 4]
const invalid4 = [6, 0, 1, 1, 1, 2, 7, 9, 6, 1, 7, 7, 7, 9, 3, 5]
const invalid5 = [5, 3, 8, 2, 0, 1, 9, 7, 7, 2, 8, 8, 3, 8, 5, 4]
// Can be either valid or invalid
const mystery1 = [3, 4, 4, 8, 0, 1, 9, 6, 8, 3, 0, 5, 4, 1, 4]
const mystery2 = [5, 4, 6, 6, 1, 0, 0, 8, 6, 1, 6, 2, 0, 2, 3, 9]
const mystery3 = [6, 0, 1, 1, 3, 7, 7, 0, 2, 0, 9, 6, 2, 6, 5, 6, 2, 0, 3]
const mystery4 = [4, 9, 2, 9, 8, 7, 7, 1, 6, 9, 2, 1, 7, 0, 9, 3]
const mystery5 = [4, 9, 1, 3, 5, 4, 0, 4, 6, 3, 0, 7, 2, 5, 2, 3]
// An array of all the arrays above
const batch = [valid1, valid2, valid3, valid4, valid5, invalid1, invalid2, invalid3, invalid4, invalid5, mystery1, mystery2, mystery3, mystery4, mystery5];
isValidCard = (array) => {
let copy = [...array];
const last = copy.pop();
copy.reverse();
copy = copy.map((dig, i) => ((i % 2 === 0 ? dig * 2 : dig)));
copy = copy.map(dig => (dig > 9 ? dig - 9 : dig));
const sum = copy.reduce((acc, curr) => acc + curr);
return ((sum + last) % 10 === 0);
}
findInvalidCards = (array) => {
const validList = [];
const invalidList = [];
array.forEach(card => {
if (isValidCard(card)) {
validList.push(card);
} else {
invalidList.push(card);
}
});
console.log('valid cards', validList);
console.log('invalid cards', invalidList);
}
findInvalidCards(batch);

I think your issue is this line:
let tempArr = array; //Copies the values of the array passed into parameters
According to your comment you want to copy the array, but just assigning it to another variable does not copies it. In order to copy just so something like this:
let copy = array.slice(0);
/* or (will not work for large arrays) */
let copy = [...array];

// All valid credit card numbers
const valid1 = [4, 5, 3, 9, 6, 7, 7, 9, 0, 8, 0, 1, 6, 8, 0, 8];
const valid2 = [5, 5, 3, 5, 7, 6, 6, 7, 6, 8, 7, 5, 1, 4, 3, 9];
const valid3 = [3, 7, 1, 6, 1, 2, 0, 1, 9, 9, 8, 5, 2, 3, 6];
const valid4 = [6, 0, 1, 1, 1, 4, 4, 3, 4, 0, 6, 8, 2, 9, 0, 5];
const valid5 = [4, 5, 3, 9, 4, 0, 4, 9, 6, 7, 8, 6, 9, 6, 6, 6];
// All invalid credit card numbers
const invalid1 = [4, 5, 3, 2, 7, 7, 8, 7, 7, 1, 0, 9, 1, 7, 9, 5];
const invalid2 = [5, 7, 9, 5, 5, 9, 3, 3, 9, 2, 1, 3, 4, 6, 4, 3];
const invalid3 = [3, 7, 5, 7, 9, 6, 0, 8, 4, 4, 5, 9, 9, 1, 4];
const invalid4 = [6, 0, 1, 1, 1, 2, 7, 9, 6, 1, 7, 7, 7, 9, 3, 5];
const invalid5 = [5, 3, 8, 2, 0, 1, 9, 7, 7, 2, 8, 8, 3, 8, 5, 4];
const invalidCredit = [invalid1, invalid2, invalid3, invalid4, invalid5]
// Can be either valid or invalid
const mystery1 = [3, 4, 4, 8, 0, 1, 9, 6, 8, 3, 0, 5, 4, 1, 4];
const mystery2 = [5, 4, 6, 6, 1, 0, 0, 8, 6, 1, 6, 2, 0, 2, 3, 9];
const mystery3 = [6, 0, 1, 1, 3, 7, 7, 0, 2, 0, 9, 6, 2, 6, 5, 6, 2, 0, 3];
const mystery4 = [4, 9, 2, 9, 8, 7, 7, 1, 6, 9, 2, 1, 7, 0, 9, 3];
const mystery5 = [4, 9, 1, 3, 5, 4, 0, 4, 6, 3, 0, 7, 2, 5, 2, 3];
// An array of all the arrays above
const batch = [valid1, valid2, valid3, valid4, valid5, invalid1, invalid2, invalid3, invalid4, invalid5, mystery1, mystery2, mystery3, mystery4, mystery5];
// Add your functions below:
const validateCred = (arr) => {
let reversedArr = arr.reverse();
let oddOccurrences = [];
reversedArr.forEach((value, i) => i % 2 ? oddOccurrences.push(value *= 2) : oddOccurrences.push(value));
const checking = oddOccurrences.map((greater) => (greater > 9 ? (greater -= 9) : greater));
const sum = checking.reduce((acc, num) => {
return acc + num
}, 0)
// Conditional check
if (sum % 10 === 0)
return 'valid'
else return 'invalid'
}
console.log(validateCred([4, 5, 3, 9, 6, 8, 9, 8, 8, 7, 7, 0, 5, 7, 9, 8]));
findInvalidCards = (newArr) => {
const invalidList = [];
const validList = [];
for (let i = 0; i < newArr.length; i += 15) {
// inner loop
for (let j = 0; j < newArr.length; j++) {
validateCred(newArr[j]) === 'invalid' ? invalidList.push(newArr[j]) : validList.push(newArr[j]);
}
};
console.log(invalidList)
}
findInvalidCards(batch);

Splice Function in Javascript is adding 4 empty rows to my array?

I want to remove all the rows whose length is less than some value. I'am using Splice function in javascript to do this.
for (var i = 0; i < table.length; i++) {
if (table[i].length<=6) {
table.splice(i, 1);
}
}
but two rows with length:0 are being added at the beginning and at the end of my array this is the actual array
extra rows added after being spliced
whis is this happening?
how can i get rid of it?

I suggest to splice from the end to start, because if an element is spliced, the following elements are move a place in front of the array.
var table = [
[0, 1, 2, 3, 4, 5],
[],
[0],
[],
[],
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13],
[0, 1, 2, 3, 4, 5, 6, 7],
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9],
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9],
[0, 1, 2, 3, 4, 5, 6, 7, 8],
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9],
[0],
[0],
[],
[],
[1]
],
i = table.length;
while (i--) {
if (table[i].length <= 6) {
table.splice(i, 1);
}
}
console.log(table);

Try with this:
for (var i = 0; i < table.length; i++) {
if (table[i].length<=6) {
table.splice(i, 1);
i--;
}
}
After deleting a row you have to decrease the index to the array because the elements of the array have been shifted by the precious removal.

JS/Node: A function that takes a number N and returns an array with the values [0, 1, ... N-1]

I am pretty sure such a function exists in some library/NPM module, alas, my attempts to find one have failed.
I am looking for something along the line of the range() function in this snippet:
var a = range(4);
expect(a).toEqual([0, 1, 2, 3]);

http://underscorejs.org/#range
_.range(10);
=> [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
_.range(1, 11);
=> [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
_.range(0, 30, 5);
=> [0, 5, 10, 15, 20, 25]
_.range(0, -10, -1);
=> [0, -1, -2, -3, -4, -5, -6, -7, -8, -9]
_.range(0);
=> []

You can create one yourself with this oneliner (Source: Creating range in JavaScript - strange syntax)
function range(end) {
return Array.apply(null, {length: end}).map(Number.call, Number);
}
console.log(range(4));
// [ 0, 1, 2, 3 ]

Underscore's implementation of range:
function range(start, stop, step) {
if (arguments.length <= 1) {
stop = start || 0;
start = 0;
}
step = arguments[2] || 1;
var length = Math.max(Math.ceil((stop - start) / step), 0);
var idx = 0;
var range = new Array(length);
while(idx < length) {
range[idx++] = start;
start += step;
}
return range;
};
Usage:
// stop 10
range(10); //[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
// start 5, stop 10
range(5, 10); //[5, 6, 7, 8, 9]
// start 1, stop 10, step 2
range(1, 10, 2); //[1, 3, 5, 7, 9]

Counting array elements and sort descending by count

Array:
5, 5, 5, 9, 4, 2, 2, 2, 2, 2, 3, 3, 3, 3
Ideal Output:
2, 3, 5, 9, 4
PHP made this easy with array_count_values() and arsort(), but javascript is proving a little tougher. Any help?
Also, what about returning it containing the counts as well? For future needs

Count unique entries, create an array of uniques, then sort based upon counts
function count(arr) { // count occurances
var o = {}, i;
for (i = 0; i < arr.length; ++i) {
if (o[arr[i]]) ++o[arr[i]];
else o[arr[i]] = 1;
}
return o;
}
function weight(arr_in) { // unique sorted by num occurances
var o = count(arr_in),
arr = [], i;
for (i in o) arr.push(+i); // fast unique only
arr.sort(function (a, b) {
return o[a] < o[b];
});
return arr;
}
weight([1, 3, 3, 5, 5, 5, 2, 2, 2, 2]);
// one 1, two 3s, three 5s, four 2s
// [2, 5, 3, 1]
You example has both one 9 and one 4, so if you want the order defined, more work would be necessary. Otherwise;
weight([5, 5, 5, 9, 4, 2, 2, 2, 2, 2, 3, 3, 3, 3]);
// [2, 3, 5, 4, 9]
To produce an Array of Objects
function weight(arr_in) { // unique sorted by num occurances
var o = count(arr_in),
arr = [], i;
for (i in o) arr.push({value: +i, weight: o[i]}); // fast unique only
arr.sort(function (a, b) {
return a.weight < b.weight;
});
return arr;
}
var result = weight([5, 5, 5, 9, 4, 2, 2, 2, 2, 2, 3, 3, 3, 3]);
/* [
{"value": 2, "weight": 5},
{"value": 3, "weight": 4},
{"value": 5, "weight": 3},
{"value": 4, "weight": 1},
{"value": 9, "weight": 1}
] */
Now, to get the value at index i, you do result[i].value, and for it's weighting result[i].weight.