How to make a for loop dynamic? - javascript

I am have 2 arrays like [2,3] and [1000,1200,500,600,1600] .
I need to write a for loop for this like.
1.start index from 0 and end index at 2.
2.start time from 2 and end index with sum of first 2 element (2+3)= 5.
var arr = [2,3];
for(var i = 0; i<arr.length;i++)
{
//this loop runs 2 time
for(var j = 0 ; j < 2 ; j++)//for the first time
for(var j = 2 ; j < 5 ; j++)//for the second time
}
How to make this dynamic for loop? Can someone please help me code?


This would do what you want and would be extendible.
var arr = [2,3];
var sum = 0;
for(var i = 0; i<arr.length;i++)
{
sum += arr[i]
if (i === 0) {
for(var j = 0 ; j < arr[0] ; j++)
// Do first thing
}
if (i > 0) {
for(var j = arr[0] ; j < sum ; j++)
// Do second thing
}
}


Hope you are expecting this.
var arr = [2, 3];
for (var i = 0; i < arr.length; i++) {
//this loop runs 2 time
if (i == 0) {
//for the first time
for (var j = 0; j < arr[0]; j++) { }
} else if (i == 1) {
//for the second time
var totalSum = arr[0] + arr[1];
for (var j = arr[0]; j < totalSum; j++) //for the second time
{ }
}
}


If you want it to be generic, i.e. you have the array arr containing counts of elements to process, you could do it like this:
var arr = [2,3];
// k is the index into the second array, initialize to 0 here
for(var i = 0, k = 0; i < arr.length;i++)
{
//this loop runs for each element in the arr[] array
for(var j = 0 ; j < i; j++, k++) // increment k
{
// k is now the value you want:
// first time through the loop 0, 1
// second time through the loop 2, 3, 4
}
}
Another tweak would be to just keep track of the start element if it's important for j to be the value:
var arr = [2,3];
var start = 0;
for(var i = 0; i < arr.length; i++)
{
var end = start + arr[i]; // end is 2,5 in sample
for(var j = start ; j < end; j++)
{
// first time through the loop 0, 1
// second time through the loop 2, 3, 4
}
start = end; // now start at the next index, 0,2 in sample
}


Do something like this:
var k = 0;
for(var j = 0 ; j < 2 ; j++) {
k+=arr[j];
}//for the first time
for(var i = 2 ; i < k ; i++) {
//other code
}

Related

Push value in multi dimensional object array - Typescript [duplicate]

I'm trying to push to a two-dimensional array without it messing up, currently My array is:
var myArray = [
[1,1,1,1,1],
[1,1,1,1,1],
[1,1,1,1,1]
]
And my code I'm trying is:
var r = 3; //start from rows 3
var c = 5; //start from col 5
var rows = 8;
var cols = 7;
for (var i = r; i < rows; i++)
{
for (var j = c; j < cols; j++)
{
myArray[i][j].push(0);
}
}
That should result in the following:
var myArray = [
[1,1,1,1,1,0,0],
[1,1,1,1,1,0,0],
[1,1,1,1,1,0,0],
[0,0,0,0,0,0,0],
[0,0,0,0,0,0,0],
[0,0,0,0,0,0,0],
]
But it doesn't and not sure whether this is the correct way to do it or not.
So the question is how would I accomplish this?

You have some errors in your code:
Use myArray[i].push( 0 ); to add a new column. Your code (myArray[i][j].push(0);) would work in a 3-dimensional array as it tries to add another element to an array at position [i][j].
You only expand (col-d)-many columns in all rows, even in those, which haven't been initialized yet and thus have no entries so far.
One correct, although kind of verbose version, would be the following:
var r = 3; //start from rows 3
var rows = 8;
var cols = 7;
// expand to have the correct amount or rows
for( var i=r; i<rows; i++ ) {
myArray.push( [] );
}
// expand all rows to have the correct amount of cols
for (var i = 0; i < rows; i++)
{
for (var j = myArray[i].length; j < cols; j++)
{
myArray[i].push(0);
}
}

In your case you can do that without using push at all:
var myArray = [
[1,1,1,1,1],
[1,1,1,1,1],
[1,1,1,1,1]
]
var newRows = 8;
var newCols = 7;
var item;
for (var i = 0; i < newRows; i++) {
item = myArray[i] || (myArray[i] = []);
for (var k = item.length; k < newCols; k++)
item[k] = 0;
}

You have to loop through all rows, and add the missing rows and columns. For the already existing rows, you loop from c to cols, for the new rows, first push an empty array to outer array, then loop from 0 to cols:
var r = 3; //start from rows 3
var c = 5; //start from col 5
var rows = 8;
var cols = 7;
for (var i = 0; i < rows; i++) {
var start;
if (i < r) {
start = c;
} else {
start = 0;
myArray.push([]);
}
for (var j = start; j < cols; j++) {
myArray[i].push(0);
}
}

Iterating over two dimensions means you'll need to check over two dimensions.
assuming you're starting with:
var myArray = [
[1,1,1,1,1],
[1,1,1,1,1],
[1,1,1,1,1]
]; //don't forget your semi-colons
You want to expand this two-dimensional array to become:
var myArray = [
[1,1,1,1,1,0,0],
[1,1,1,1,1,0,0],
[1,1,1,1,1,0,0],
[0,0,0,0,0,0,0],
[0,0,0,0,0,0,0],
[0,0,0,0,0,0,0],
];
Which means you need to understand what the difference is.
Start with the outer array:
var myArray = [
[...],
[...],
[...]
];
If you want to make this array longer, you need to check that it's the correct length, and add more inner arrays to make up the difference:
var i,
rows,
myArray;
rows = 8;
myArray = [...]; //see first example above
for (i = 0; i < rows; i += 1) {
//check if the index exists in the outer array
if (!(i in myArray)) {
//if it doesn't exist, we need another array to fill
myArray.push([]);
}
}
The next step requires iterating over every column in every array, we'll build on the original code:
var i,
j,
row,
rows,
cols,
myArray;
rows = 8;
cols = 7; //adding columns in this time
myArray = [...]; //see first example above
for (i = 0; i < rows; i += 1) {
//check if the index exists in the outer array (row)
if (!(i in myArray)) {
//if it doesn't exist, we need another array to fill
myArray[i] = [];
}
row = myArray[i];
for (j = 0; j < cols; j += 1) {
//check if the index exists in the inner array (column)
if (!(i in row)) {
//if it doesn't exist, we need to fill it with `0`
row[j] = 0;
}
}
}

var r = 3; //start from rows 3
var c = 5; //start from col 5
var rows = 8;
var cols = 7;
for (var i = 0; i < rows; i++)
{
for (var j = 0; j < cols; j++)
{
if(j <= c && i <= r) {
myArray[i][j] = 1;
} else {
myArray[i][j] = 0;
}
}
}

you are calling the push() on an array element (int), where push() should be called on the array, also handling/filling the array this way makes no sense
you can do it like this
for (var i = 0; i < rows - 1; i++)
{
for (var j = c; j < cols; j++)
{
myArray[i].push(0);
}
}
for (var i = r; i < rows - 1; i++)
{
for (var j = 0; j < cols; j++)
{
col.push(0);
}
}
you can also combine the two loops using an if condition, if row < r, else if row >= r

Create am array and put inside the first, in this case i get data from JSON response
$.getJSON('/Tool/GetAllActiviesStatus/',
var dataFC = new Array();
function (data) {
for (var i = 0; i < data.Result.length; i++) {
var serie = new Array(data.Result[i].FUNCAO, data.Result[i].QT, true, true);
dataFC.push(serie);
});

The solution below uses a double loop to add data to the bottom of a 2x2 array in the Case 3. The inner loop pushes selected elements' values into a new row array. The outerloop then pushes the new row array to the bottom of an existing array (see Newbie: Add values to two-dimensional array with for loops, Google Apps Script).
In this example, I created a function that extracts a section from an existing array. The extracted section can be a row (full or partial), a column (full or partial), or a 2x2 section of the existing array. A new blank array (newArr) is filled by pushing the relevant section from the existing array (arr) into the new array.
function arraySection(arr, r1, c1, rLength, cLength) {
rowMax = arr.length;
if(isNaN(rowMax)){rowMax = 1};
colMax = arr[0].length;
if(isNaN(colMax)){colMax = 1};
var r2 = r1 + rLength - 1;
var c2 = c1 + cLength - 1;
if ((r1< 0 || r1 > r2 || r1 > rowMax || (r1 | 0) != r1) || (r2 < 0 ||
r2 > rowMax || (r2 | 0) != r2)|| (c1< 0 || c1 > c2 || c1 > colMax ||
(c1 | 0) != c1) ||(c2 < 0 || c2 > colMax || (c2 | 0) != c2)){
throw new Error(
'arraySection: invalid input')
return;
};
var newArr = [];
// Case 1: extracted section is a column array,
// all elements are in the same column
if (c1 == c2){
for (var i = r1; i <= r2; i++){
// Logger.log("arr[i][c1] for i = " + i);
// Logger.log(arr[i][c1]);
newArr.push([arr[i][c1]]);
};
};
// Case 2: extracted section is a row array,
// all elements are in the same row
if (r1 == r2 && c1 != c2){
for (var j = c1; j <= c2; j++){
newArr.push(arr[r1][j]);
};
};
// Case 3: extracted section is a 2x2 section
if (r1 != r2 && c1 != c2){
for (var i = r1; i <= r2; i++) {
rowi = [];
for (var j = c1; j <= c2; j++) {
rowi.push(arr[i][j]);
}
newArr.push(rowi)
};
};
return(newArr);
};

You can also try like this.
var r = 3; //start from rows 3
var c = 5; //start from col 5
var rows = 8;
var cols = 7;
for (var i = r; i < rows; i++)
{
for (var j = c; j < cols; j++)
{
myArray.push([var[i],var[j])
}
}
this will create a 2d array for you.

<script>
let test = new Array;
for(let i = 1; i < 10; i++){
test[i] = new Array;
test[i]['type'] = 'test-type'+i;
test[i]['content'] = 'test-content'+i;
}
console.log(test);
</script>

Performance: why is the first implementation of the same algorithm significantly faster

The algorithm is taken from LeetCode: https://leetcode.com/problems/maximum-product-of-word-lengths/description/
Here is the jsperf I created (I have some local tests which gives the same result): https://jsperf.com/maximum-product-of-word-lengths
Here is the first "slow" implementation:
function maxProduct (words) {
if (!words || !words.length) return 0;
let len = words.length;
let values = [];
// console.log(values)
for (let i = 0; i < len; ++i) {
let tmp = words[i];
let num = 0, len = tmp.length;
for (let j = 0; j < len; ++j) {
num |= 1 << (tmp.charCodeAt(j) - 'a'.charCodeAt(0));
}
values[i] = {
num: num,
len: tmp.length
};
}
let maxProduct = 0;
for (let i = 0; i < len; ++i) {
for (let j = 0; j < len; ++j) {
if ((values[i].num & values[j].num) == 0) {
maxProduct = Math.max(maxProduct, values[i].len * values[j].len);
}
}
}
return maxProduct;
};
Here is the "fast" implementation:
function maxProductFast (words) {
var temp = [];
for(var i = 0; i < words.length; i++){
var tempObj = {};
tempObj.item = words[i];
var num = 0;
for(var j = 0; j < words[i].length; j++){
num |= 1 << (words[i].charCodeAt(j) - 97);
}
tempObj.num = num;
temp.push(tempObj);
}
var res = 0;
for(var i = 0; i < temp.length; i++){
for(var j = i + 1; j < temp.length; j++){
var item1 = temp[i];
var item2 = temp[j];
if((item1.num & item2.num) == 0) {
res = Math.max(res, item1.item.length * item2.item.length);
}
}
}
return res;
}

They're not the same. The second algorithm has a loop with a complexity of (n*(n+1))/2 where each progressive step is from i+1 to the length of temp. the first algorithm has a two nested for loops each with a cost of n^2. the complexity of both will reduce to O(n^2). I believe that both of these will have a similar performance with a significantly large enough set.
The reason you would do n+1 for each sub iteration is because you are trying to find the max of any pair of items. if you place your elements in a grid you will notice that any diagonal pair a_3 * a_2 = a_2 * a_3 produces the same value. you can basically halve the collection and save a few cycles.

Print prime numbers between 0 and 100

I'm trying to print all prime number between 0 and 100, but when executing this code the browser's tab just outputs nothing!!
for(var i = 2; i < 100; i++)
{
var prime = [];
for(var j = 0; j <= i; j++)
{
var p = i % j;
}
if(p != 0) prime.push(i);
else continue;
}
for(var k = 0; k < prime.length; k++)
{
document.writeln(prime[k], "<br>");
}

Try this one. I have also optimise the code (you only need to check upto sqrt(i) ).
var prime = [];
prime.push(2); //smallest prime
var flag = 0;
for(var i = 3; i < 100; i=i+2) //skip all even no
{
for(var j = 3; j*j <= i; j=j+2) //check by upto sqrt(i), skip all even no
{
if(i % j == 0) {
flag = 0;break; //not a prime, break
}
flag = 1;
}
if (flag == 1) prime.push(i); //prime, add to answer
}
for(var k = 0; k < prime.length; k++)
{
document.writeln(prime[k], "<br>");
}

Because you blank your list of primes EVERY loop cycle, move it outside the for loop

You need to make your variable prime outside of your loop
This is the code you have re-written
var prime = [];
for(var i = 2; i < 100; i++)
{
for(var j = 0; j <= i; j++)
{
var p = i % j;
}
if(p != 0) prime.push(i);
else continue;
}
for(var k = 0; k < prime.length; k++)
{
document.writeln(prime[k], "<br>");
}

I'm a fan of the sieve of Eratosthenes.
The following code should do what you wanted.
var prime = Array(101).fill(true);
for (var i = 2; i < 100; ++i){
if (prime[i]){
document.writeln(i, "<br>");
for (var j = i*i; j < 100; j += i){
prime[j] = false;
}
}
}
Or since it's only up to 100 you could just manually type the list (but, hey where's the learning if you do it that way?).

(1) Move prime outside the for loop, (2) start j at 2 and end when j < i, (3) check when p == 0 with a boolean flag and break inner loop.
var prime = []; //put prime out here so it does not reassign
for(var i = 2; i < 100; i++)
{
var isPrime = true;
for(var j = 2; j < i; j++) //start j at 2
{
var p = i % j;
if(p == 0)
{
isPrime = false;
break;
}
}
if(isPrime) prime.push(i);
}
for(var k = 0; k < prime.length; k++)
{
document.writeln(prime[k], "<br>");
}

Javascript 2D array generation doesn't work as intended

I am new here, and to programming as well. Anyway, to get in topic I wrote the following program with the purpose of generating a 2 dimensional array in JavaScript, and then displaying its elements in a table. However, in the place where the value of the i row array index was supposed to show (like 1 in first row, then 2 in the second row, etc), the number 10 shows instead. So, I'd appreciate if someone could explain what I did wrong. Here is the code:
<table border="1">
<script>
var array1 = [];
var array2 = [];
for (var i = 0; i < 10; i++) {
for (var j = 0; j < 10; j++) {
array2[j] = (i + 1) + "-" + (j + 1);
}
array1[i] = array2;
}
for (var i = 0; i < 10; i++) {
document.write("<tr>");
for (var j = 0; j < 10; j++) {
document.write("<td>" + array1[i][j] + "</td>");
}
document.write("</tr>");
}
</script>
</table>

You are adding the same array to array1, again and again. Instead you need to create new arrays every time.
var array1 = [];
for (var i = 0; i < 10; i++ ) {
var array2 = [];
for (var j = 0; j < 10; j++) {
array2[j] = (i+1) + "-" + (j+1);
}
array1[i]=array2;
}
But normally, this will be done with Array.prototype.push method, like this
var array1 = [];
for (var i = 0; i < 10; i++ ) {
var array2 = [];
for (var j = 0; j < 10; j++) {
array2.push((i+1) + "-" + (j+1));
}
array1.push(array2);
}

You can create new array each time after assigned array2 to array1, something like this
array2=[];
on
for (var i = 0; i < 10; i++ ) {
for (var j = 0; j < 10; j++) {
array2[j] = (i+1) + "-" + (j+1);
}
array1[i]=array2;
array2=[]; //created new array each time after array2 assigned
}

push() a two-dimensional array

I'm trying to push to a two-dimensional array without it messing up, currently My array is:
var myArray = [
[1,1,1,1,1],
[1,1,1,1,1],
[1,1,1,1,1]
]
And my code I'm trying is:
var r = 3; //start from rows 3
var c = 5; //start from col 5
var rows = 8;
var cols = 7;
for (var i = r; i < rows; i++)
{
for (var j = c; j < cols; j++)
{
myArray[i][j].push(0);
}
}
That should result in the following:
var myArray = [
[1,1,1,1,1,0,0],
[1,1,1,1,1,0,0],
[1,1,1,1,1,0,0],
[0,0,0,0,0,0,0],
[0,0,0,0,0,0,0],
[0,0,0,0,0,0,0],
]
But it doesn't and not sure whether this is the correct way to do it or not.
So the question is how would I accomplish this?

You have some errors in your code:
Use myArray[i].push( 0 ); to add a new column. Your code (myArray[i][j].push(0);) would work in a 3-dimensional array as it tries to add another element to an array at position [i][j].
You only expand (col-d)-many columns in all rows, even in those, which haven't been initialized yet and thus have no entries so far.
One correct, although kind of verbose version, would be the following:
var r = 3; //start from rows 3
var rows = 8;
var cols = 7;
// expand to have the correct amount or rows
for( var i=r; i<rows; i++ ) {
myArray.push( [] );
}
// expand all rows to have the correct amount of cols
for (var i = 0; i < rows; i++)
{
for (var j = myArray[i].length; j < cols; j++)
{
myArray[i].push(0);
}
}

In your case you can do that without using push at all:
var myArray = [
[1,1,1,1,1],
[1,1,1,1,1],
[1,1,1,1,1]
]
var newRows = 8;
var newCols = 7;
var item;
for (var i = 0; i < newRows; i++) {
item = myArray[i] || (myArray[i] = []);
for (var k = item.length; k < newCols; k++)
item[k] = 0;
}

You have to loop through all rows, and add the missing rows and columns. For the already existing rows, you loop from c to cols, for the new rows, first push an empty array to outer array, then loop from 0 to cols:
var r = 3; //start from rows 3
var c = 5; //start from col 5
var rows = 8;
var cols = 7;
for (var i = 0; i < rows; i++) {
var start;
if (i < r) {
start = c;
} else {
start = 0;
myArray.push([]);
}
for (var j = start; j < cols; j++) {
myArray[i].push(0);
}
}

Iterating over two dimensions means you'll need to check over two dimensions.
assuming you're starting with:
var myArray = [
[1,1,1,1,1],
[1,1,1,1,1],
[1,1,1,1,1]
]; //don't forget your semi-colons
You want to expand this two-dimensional array to become:
var myArray = [
[1,1,1,1,1,0,0],
[1,1,1,1,1,0,0],
[1,1,1,1,1,0,0],
[0,0,0,0,0,0,0],
[0,0,0,0,0,0,0],
[0,0,0,0,0,0,0],
];
Which means you need to understand what the difference is.
Start with the outer array:
var myArray = [
[...],
[...],
[...]
];
If you want to make this array longer, you need to check that it's the correct length, and add more inner arrays to make up the difference:
var i,
rows,
myArray;
rows = 8;
myArray = [...]; //see first example above
for (i = 0; i < rows; i += 1) {
//check if the index exists in the outer array
if (!(i in myArray)) {
//if it doesn't exist, we need another array to fill
myArray.push([]);
}
}
The next step requires iterating over every column in every array, we'll build on the original code:
var i,
j,
row,
rows,
cols,
myArray;
rows = 8;
cols = 7; //adding columns in this time
myArray = [...]; //see first example above
for (i = 0; i < rows; i += 1) {
//check if the index exists in the outer array (row)
if (!(i in myArray)) {
//if it doesn't exist, we need another array to fill
myArray[i] = [];
}
row = myArray[i];
for (j = 0; j < cols; j += 1) {
//check if the index exists in the inner array (column)
if (!(i in row)) {
//if it doesn't exist, we need to fill it with `0`
row[j] = 0;
}
}
}

var r = 3; //start from rows 3
var c = 5; //start from col 5
var rows = 8;
var cols = 7;
for (var i = 0; i < rows; i++)
{
for (var j = 0; j < cols; j++)
{
if(j <= c && i <= r) {
myArray[i][j] = 1;
} else {
myArray[i][j] = 0;
}
}
}

you are calling the push() on an array element (int), where push() should be called on the array, also handling/filling the array this way makes no sense
you can do it like this
for (var i = 0; i < rows - 1; i++)
{
for (var j = c; j < cols; j++)
{
myArray[i].push(0);
}
}
for (var i = r; i < rows - 1; i++)
{
for (var j = 0; j < cols; j++)
{
col.push(0);
}
}
you can also combine the two loops using an if condition, if row < r, else if row >= r

Create am array and put inside the first, in this case i get data from JSON response
$.getJSON('/Tool/GetAllActiviesStatus/',
var dataFC = new Array();
function (data) {
for (var i = 0; i < data.Result.length; i++) {
var serie = new Array(data.Result[i].FUNCAO, data.Result[i].QT, true, true);
dataFC.push(serie);
});

The solution below uses a double loop to add data to the bottom of a 2x2 array in the Case 3. The inner loop pushes selected elements' values into a new row array. The outerloop then pushes the new row array to the bottom of an existing array (see Newbie: Add values to two-dimensional array with for loops, Google Apps Script).
In this example, I created a function that extracts a section from an existing array. The extracted section can be a row (full or partial), a column (full or partial), or a 2x2 section of the existing array. A new blank array (newArr) is filled by pushing the relevant section from the existing array (arr) into the new array.
function arraySection(arr, r1, c1, rLength, cLength) {
rowMax = arr.length;
if(isNaN(rowMax)){rowMax = 1};
colMax = arr[0].length;
if(isNaN(colMax)){colMax = 1};
var r2 = r1 + rLength - 1;
var c2 = c1 + cLength - 1;
if ((r1< 0 || r1 > r2 || r1 > rowMax || (r1 | 0) != r1) || (r2 < 0 ||
r2 > rowMax || (r2 | 0) != r2)|| (c1< 0 || c1 > c2 || c1 > colMax ||
(c1 | 0) != c1) ||(c2 < 0 || c2 > colMax || (c2 | 0) != c2)){
throw new Error(
'arraySection: invalid input')
return;
};
var newArr = [];
// Case 1: extracted section is a column array,
// all elements are in the same column
if (c1 == c2){
for (var i = r1; i <= r2; i++){
// Logger.log("arr[i][c1] for i = " + i);
// Logger.log(arr[i][c1]);
newArr.push([arr[i][c1]]);
};
};
// Case 2: extracted section is a row array,
// all elements are in the same row
if (r1 == r2 && c1 != c2){
for (var j = c1; j <= c2; j++){
newArr.push(arr[r1][j]);
};
};
// Case 3: extracted section is a 2x2 section
if (r1 != r2 && c1 != c2){
for (var i = r1; i <= r2; i++) {
rowi = [];
for (var j = c1; j <= c2; j++) {
rowi.push(arr[i][j]);
}
newArr.push(rowi)
};
};
return(newArr);
};

You can also try like this.
var r = 3; //start from rows 3
var c = 5; //start from col 5
var rows = 8;
var cols = 7;
for (var i = r; i < rows; i++)
{
for (var j = c; j < cols; j++)
{
myArray.push([var[i],var[j])
}
}
this will create a 2d array for you.

<script>
let test = new Array;
for(let i = 1; i < 10; i++){
test[i] = new Array;
test[i]['type'] = 'test-type'+i;
test[i]['content'] = 'test-content'+i;
}
console.log(test);
</script>

Categories

Resources